What's new in thtk 2:

* thdat: A bug which made compression for TH07 fail has been
  fixed.
* thdat: Extraction can now use parallel execution.
* thdat: Compression efficiency has been improved beyond
  that of the official archives.
* thdat: Compression times have been reduced by about 40%.
* thecl: The version option must now be specified for
  compilation and dumping.
* thecl: The syntax for the difficulty mask has been changed.
* thecl: Parse stack-based expressions for games other than
  TH10.
* thecl: New type-specific operators have been added which
  take values of any kind and give back a value of the kind
  specified by the operator.  $+ is an addition returning an
  integer value, while %+ is an addition returning a
  floating-point value.  In case the generic operator is
  used (+), the return value depends on the value passed to
  it:  If both are integer, the return value is integer as
  well, if any is floating, the return value is floating.
* thecl: Expressions can now be used as parameters to
  instructions.  These expressions must be contained within
  $() or %(), and are replaced by [-1] or [-1.0f]
  respectively.  The actual expression is output before the
  instruction it is passed to.
* thecl: Variables are supported, these are defined in the
  argument list of a function, or in the body by a var
  statement.  When using the variables, they must be
  prefixed by $ or % in order to know which type is being
  requested.  The dumper attempts to figure out the arity of
  functions, and gives variables automatic names.
