set precond outside transitions loop, use precond
typofix: order of args and returned tuple
adjust logging

- reduce polytope.polytope, abstract.feasible logging by converting: info -> debug messages
- some info in synth, gr1cint
- introduce logging in get_transitions, merge_partitions of tank_functions
style towards pep8
shorter lines, style
mv spec.parse -> spec.ast
extract pyparsing usage from spec.ast to spec.parse
import pyparsing as pp
mv spec.parser -> spec.pyparser
extract pyparsing-independent functions from spec.pyparser to spec.parse
update module docstrings to new contents
make spec.parser independent of pyparsing
new: spec.plyparser

parser generator using PLY (Lex/Yacc), orders of magnitude faster than pyparsing
add option to select between ply and pyparsing
update imports from spec
replace parse -> parser in form
import pyparsing as pp in jtlvint
remnant replacement: parse -> ast
recognize &, | tokens in ply parser
make ply the default parser generator