Currently the HTTP handlers are attached to an API mux which is created inside
Setup(). In the future, we'll want to split this out so a single mux can have
both sync and clientapi handlers attached to it.

This distinguishes them from tools like 'kafka-producer'
which are not required to run a dendrite server.

The prefix also groups together the dendrite binaries nicely
on `ls` as well as making it nicer to tab-complete.

* Update gomatrixserverib dep

* Use helper functions when creating rooms

* Use gomatrixserverlib.StateKeyTuple

* Add option to stop processing input after a given number of messages

* Implement state conflict resolution

This involves:
 - Parsing the HTTP request
 - Requesting auth events from the roomserver via the Query API
 - Building the event
 - Doing auth checks on the event
 - Sending it to the roomserver input log

* Tool for creating room events

Previously, the error responses:
 - were not valid matrix errors (no `errcode`)
 - returned the `err.Error()` message which may contain sensitive information.
 - did not get logged (at all, let alone set the level correctly).

Now the error responses:
 - return valid matrix errors (`M_UNKNOWN`)
 - return a generic "Internal Server Error" string
 - get logged at `ERROR` level.

* Return the requested portions of current state in the query API

* Use Unique from github.com/matrix-org/util

* rewrite bulkSelectFilteredStateBlockEntries to use append for clarity

* Add test for stateKeyTupleSorter

* Replace current with a new StateEntryList rather than individually setting the fields

This should:
    1) Make the input package a bit cleaner.
    2) Allow use to reuse the state reading code from the query package.

* Update github.com/matrix-org/util

* Use Unique from github.com/matrix-org/util

* Add helper method for preparing lists of statements.

* Add method for calculating the room state after a list of events

* Fill out AddsState and RemovesState fields in the output event

* comment on return value

* Fix whitespace

* Clarify the meaning of LastEventIDSent

* Be more explicit on what the snapshot is

* Fix comments

* Comment on why we want the state after the previous events

* Start implementing a query API for go using net/rpc

* Use a conventional JSON POST API rather than go net/rpc

net/rpc doesn't automatically handle reconnecting and we have better
logging and metrics infrastructure for monitoring HTTP apis.

* Implement the query API and add it to the integration tests

* Increase the timeout, travis seems to be a bit slow

* Clarify that state events are the things that are not returned if they are not requested

* Add utility function for converting arrays of numeric event IDs to pq Int64Arrays

* Warn people against requesting empty state keys by accident

* Add integration tests for roomserver to travis

* Try setting the dist trusty to see if that helps with postgres

* Pretty print the test input JSON

* Add comment as to why we are using trusty

Typo

* Track which events have been sent and the last event sent for each room

* Write output events

* comment that an event could be sent twice

* Get the SQL working, and make it more idempotent

* Marshal and Unmarshal methods for roomserver input api

* Comments for why we don't json.marshal the InputRoomEvent directly

* More comments

* s/m.room.create/the first event/

* Track which events are the latest events in the room.

Terse function names are used to make usage not stutter. For example:

```go
err := error.Forbidden("you shall not pass")
```

At the moment they are all the same fundamental `MatrixError` type. This will
be bad if we ever want to `switch` based on the kind of error. I'm hoping we
won't ever need to introspect into errors like this: ideally these errors would
be created purely for immediately being returned in an HTTP response.

`MatrixError` implements the `error` interface.