refactoring / style fixes

* make all code comply to checkstyle
* move all math-related code into the math package
wip: work on gf(2^257)

Only work on RabinIDS for now and try to find out where the problems lie

So far, the following has been identified with this simple prototype:

 * simple gf(257) is too slow to even wait for an result with BW-Decoder
 * there seems to be an error when using 1,1,1 as yValues combined with
   1,2,3 for xValues
 * code/decode step is needed and not that easy (we dont' want to create
   full input/output array duplicates)
 * more work will follow
wip: make gf(257) work with rabinIDS+erasure deocoder

* removed lots of gf(256)isms. This should also fix some
  problems with BCGF256
* this still does not work with rabinids and bwdecoder.
  This combination produces an infinite loop with data=1
fix: berlekamp-welch with gf(257) and optimizations

* again this was a gf(2^n)-ism: add ain't the same as sub within
  gf(257)
* removed some (by now) unneeded assertions
* added better unit tests for gf-arithmentic (to allow for removed
  assertions)
* PolyHash should check that input has the right format
* pre-compute some exp/pows for gf(257)
Merge pull request #22 from andreashappe/master

make algorithms better suited for additional gf-classes