Two rules (Fraction, Power simplification)

1. Simplifies [0 / term] -> 0
2. Simplifies e.g. [exp(x) * exp(y)] -> [exp(x+y)]
Introduced explicit rules for Ln/Log
Re-sorted show clauses
Some improvements with Log
Fixed problem with certain term - reworked Simplify a bit

J. Bucher tested Simplify and noticed that

((4-x^5) (3 y^4))/(2.5 x y^3)

was simplified to

((4-x^5)×1.2 y^4)/(x y^3)

although it should rather be

(1.2 (4-x^5) y)/x

This fix enables Simplify to transform such terms with a higher
complexity. The result delivered in this revision is

1.2 * (4.0 - (x)^(5.0)) * (x)^(-1.0) * y
Better sorting (regression)
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
Symmath is now the only exposed module
Read-eval-print-loop for testing simplify
Release IV.1

Better cabal build file