Remove eqtype declaration for term type

Delete trailing whitespace in src/

add manual pattern match heuristic / improve exhaustive one

Implement a new pattern match heuristic that allows manually
specifying in which order to do case splits. This one prints
a lot of debugging information in order to allow the user to
make decent choices. The techniques for producing this debug
have also been added to the exhaustive tactic. It now prints
debugging information on how far the exhaustive search
progressed and on intermediate results

Fallback on "classic" cases heuristic when Induction.mk_induction raises an exception. This closes issue #127.

Partial fix for issue #127.

The definition of "remove_parse_stack" now works for the "classic heuristic" (set using PmatchHeuristics) but still fails for the "default". For the time being, an argument could be making the "classic" the default again, since it appears to be more stable.

The pertinent change was in Defn.wfrec_eqns, where "elim_triv_literal_CONV" is now incorporated into "rule". Other changes are tidy-ups.

cleanup of Pmatch

Following a suggestion of Anthony, I cleaned-up the interface of Pmatch.
To this end, I moved much of the heuristics-code to a new library called
PmatchHeuristics. This new library is used by Pmatch. This allows to
clean-up the code and interface of Pmatch. If less frequently used functions
are needed, the library PmatchHeuristics has to be used now.