The new return value is the number of keys existing, among the ones
specified in the command line, counting the same key multiple times if
given multiple times (and if it exists).

See PR #2667.

GEOHASH, GEOPOS and GEODIST where declared as commands not accepting
keys, so the Redis Cluster redirection did not worked.

Close #2671.

Rationale:

1. The commands look like internals exposed without a real strong use
case.
2. Whatever there is an use case, the client would implement the
commands client side instead of paying RTT just to use a simple to
reimplement library.
3. They add complexity to an otherwise quite straightforward API.

So for now KILLED ;-)

Instead of successive divisions in iteration the new code uses bitwise
magic to interleave / deinterleave two 32bit values into a 64bit one.
All tests still passing and is measurably faster, so worth it.

I'm not a strong believer in multiple syntax for the same stuff, so
now units can be specified only as m, km, ft, mi.

Stack traces produced by Redis on crash are the most useful tool we
have to fix non easily reproducible crashes, or even easily reproducible
ones where the user just posts a bug report and does not collaborate
furhter.

By declaring functions "static" they no longer show up in the stack
trace.

In Redis MULTIWORDCOMMANDNAME are mapped to functions where the command
name is all lowercase: multiwordcommandnameCommand().

If GEOENCODE must be our door to enter the Geocoding implementation
details and do fancy things client side, than return the scores as well
so that we can query the sorted sets directly if we wish to do the same
search multiple times, or want to compute the boxes in the client side
to refine our search needs.

Can't immagine how this is useful in the context of the API exported by
Redis, and we are always in time to add more bloat if needed, later.

The GIS standard and all the major DBs implementing GIS related
functions take coordinates as x,y that is longitude,latitude.
It was a bad start for Redis to do things differently, so even if this
means that existing users of the Geo module will be required to change
their code, Redis now conforms to the standard.

Usually Redis is very backward compatible, but this is not an exception
to this rule, since this is the first Geo implementation entering the
official Redis source code. It is not wise to try to be backward
compatible with code forks... :-)

Close #2637.

The returned step was in some case not enough towards normal
coordinates (for example when our search position was was already near the
margin of the central area, and we had to match, using the east or west
neighbor, a very far point). Example:

    geoadd points 67.575457940146066 -62.001317572780565 far
    geoadd points 66.685439060295664 -58.925040587282297 center
    georadius points 66.685439060295664 -58.925040587282297 200 km

In the above case the code failed to find a match (happens at smaller
latitudes too) even if far and center are at less than 200km.

Another fix introduced by this commit is a progressively larger area
towards the poles, since meridians are a lot less far away, so we need
to compensate for this.

The current implementation works comparably to the Tcl brute-force
stress tester implemented in the fuzzy test in the geo.tcl unit for
latitudes between -70 and 70, and is pretty accurate over +/-80 too,
with sporadic false negatives.

A more mathematically clean implementation is possible by computing the
meridian distance at the specified latitude and computing the step
according to it.

We set random points in the world, pick a random position, and check if
the returned points by Redis match the ones computed by Tcl by brute
forcing all the points using the distance between two points formula.

This approach is sounding since immediately resulted in finding a bug in
the original implementation.

1. We no longer use a fake client but just rewriting.
2. We group all the inserts into a single ZADD dispatch (big speed win).
3. As a side effect of the correct implementation, replication works.
4. The return value of the command is now correct.

This commit simplifies the implementation in a few ways:

1. zsetScore implementation improved a bit and moved into t_zset.c where
   is now also used to implement the ZSCORE command.

2. Range extraction from the sorted set remains a separated
   implementation from the one in t_zset.c, but was hyper-specialized in
   order to avoid accumulating results into a list and remove the ones
   outside the radius.

3. A new type is introduced: geoArray, which can accumulate geoPoint
   structures in a vector with power of two expansion policy. This is
   useful since we have to call qsort() against it before returning the
   result to the user.

4. As a result of 1, 2, 3, the two files zset.c and zset.h are now
   removed, including the function to merge two lists (now handled with
   functions that can add elements to existing geoArray arrays) and
   the machinery used in order to pass zset results.

5. geoPoint structure simplified because of the general code structure
   simplification, so we no longer need to take references to objects.

6. Not counting the JSON removal the refactoring removes 200 lines of
   code for the same functionalities, with a simpler to read
   implementation.

7. GEORADIUS is now 2.5 times faster testing with 10k elements and a
   radius resulting in 124 elements returned. However this is mostly a
   side effect of the refactoring and simplification. More speed gains
   can be achieved by trying to optimize the code.

For some reason the Geo PR included disabling the fact that Redis is
compiled with optimizations. Apparently it was just @mattsta attempt to
speedup the modify-compile-test iteration and there are no other
reasons.

Now used both in geo.c and t_zset to provide ZSCORE.