net plugin and genesis-timestamp

not quite perfect yet.

also adding interpretation of a --genesis-timestamp command line option to override that provided in the genesis.json file.
format of the timestamp value is either the ISO format yyyy-mm-ddThh:mm:ss (UTC) or the word now for using the current time
as the timestamp.

- implement a large part of example exchange contract

fix Name() conversion
names now support any characters and those outside the 32 defined are
treated the same as '.'.

TODO: replace Makefile with CMakeLists

Adding more p2p functionality, including enhancing the synchronizatio…

Adding more p2p functionality, including enhancing the synchronization of new joiners, and the processing of peer addresses.

It builds, but the tests are a complete mess.

Also define some types and stuff for #7... Lost in the mix.

All transactions must declare a list of permissions they utilize. The
chain now checks that the signatures are present to satisfy these
permissions, at least theoretically (only partially tested). As the
transaction is evaluated and applied, the message handlers will check
that the required permissions were declared on the transaction.

Also, define the logic to check that an authority is satisfied (only this
part is tested so far)

TODO: Test that transactions are rejected if they do not bear sufficient
signatures
TODO: Make message handlers check the declared permissions are sufficient,
and reject the transaction if they are not.

Move the tests that are slow to execute into a separate binary

Incremental p2p networking