Added some paragraphs to the README

About "Comparison", "Modularization", "Testing".
Merge branch 'next'
Re-sorted show clauses
Fixed "if" indentation for cabal

Alternative: Use Extension "DoAndIfThenElse"
Added re-exporting Symmath module as well as a Cabal file
Added Setup.hs for people w/o cabal-install
Release IV.

New features:
- Improved simplify
- Small fixes in Terms
- *whoohoo* Cabal setup