interface split to ‘map’ and ‘set’
added documentation
array: added array_tail() operation

The engine is responsible for central managemento of resources and work
distribution. This allows to spawn multiple loops.

The engine configuration / interface is based on Lua 5.1-5.2, including
a RPC and a simple CLI interface. This is going to be the core of configuration
later on.

the build system now doesn't always relink targets

refs #7