Usual functions' names & simple fractions

[Kerl13]

I added two filters suggested in the TODO list:

• nice-frac converts simple fractions like (n / k) to \frac{n}{k} when in a math environment
• usual-fun add the leading \ before usual functions' names (cos, sin, tan, cotan, arccos, arcsin, arctan, exp, log)

I modified the Makefile to compile the filters with ghc and also fix a problem with input and output files (may be a problem due to my old version of the make command). Packages 'pandoc' and 'regex-compat' are required

[Phyks]

Could you add a .cabal file listing required packages?

[Kerl13]

Done :)