Add initial implementation for memory input stream
Remove foreign threads and mutexes

 * Common Lisp library should be used instead. The foreign
   threads implementation did not work well in combination
   with ECL's pthread usage.
Fix portability issues presented on macOS
Add nickname for testing package, add test for thread callbacks
Implement part of the Thread API

 * Helper macro for easily creating callbacks to be
   run inside a thread: MAKE-THREAD-CALLBACK.
Remove silent loading from unit tests

Silently loading the libraries for unit testing removes
few unnecessary lines of output. However, on some
OS/implementation combinations this can lead to the
loading failing; probably because Quicklisp binds
the output stream(s) to a dummy broadcast-stream.
This happens for example on Debian GNU/Linux with

One way to fix this would be to remove the silent loading
conditionally only for some implementations. However, this
current change is simpler and should work on all
OS/implementation combinations without problems.
Fix few typos, install a package on test runner
Implement more of the System API
Implement more of the System API
Implement more of time related System API
Implement more of time related System API
Implement more of the system API vector related helpers
Implement more of the System API
Export more symbols, add documentation and tests

 * Export CSFML variable *TIME-ZERO*.
 * Export additional helper predicate TIME-EQUAL-P
   for comparing CSFML :TIME values.
Export more of System, add API.org, fix error reports
Add initial commit