Moved non-essential parts of docs to wiki.

Removed glossary, links to other redo implementations and articles about
build systems, and some other docs concerning the background (rather
than the functioning) from the fix inline documentation, and placed it
on the fix wiki page instead.
Added reading of config file. Added '--add-path'.

* Added reading of '.fixrc' config file (only supported option right
  now is 'core.addPath').

* Moved initialization of options into run() - it was prematurely
  initialized, when loaded by the test suite by means of require +
  import.

* Added documentation for 'core.addPath' and '--add-path', the
  configuration file in general.

* Added $FIX_PWD (the name of the current directory when invoked).