deleting a path in the store.
* Allow absolute paths in Nix expressions.
* Get nix-prefetch-url to work again.
* Various other fixes.

  configuration.
* Status queries.

* Replace all directory reading code by a generic readDirectory()
  function.

  that it can be used by multiple programs.

* Several bug fixes in the grammar.
* Allow one-line comments (#... and //...) to end in EOF.

* More refactoring.

* More refactoring.

* Add some rejections and lexical restrictions to the grammar to make
  this work. 

  turned out to be a huge performance bottleneck (the text to printed
  would always be evaluated, even when it was above the verbosity
  level).  This reduces fix-ng execution time by over 50%.

  gprof(1) is very useful. :-)

* Logical operators (!, &&, ||, ->).

  substitutions, Fix terms are very large when printed as trees (in 
  memory, they are quite compact due to sharing).

  The ATerm library doesn't search the heap for pointers to ATerms
  when garbage collecting.  As a result, C++ containers such as
  `map<ATerm, ATerm>' will cause pointer to be hidden from the garbage
  collector, causing crashes.  Instead, we now use ATermTables.

  semicolons instead of comma's.  Final semicolon in the set is optional.

  attribute set.