TODO
  * sparse vector (unordered_map) -> where to store?
  * parser
  * Rule -> ChartItem -> Node ?
  * viterbi path/string
  * k-best
  * other semirings
  * include language model
  * compress/hash words/feature strings?


Dependencies:
 * MessagePack for object serialization [1]
 * kenlm language model [2]
 

This is Linux only.


[1] http://msgpack.org
[2] http://kheafield.com/code/kenlm/

http://math.nist.gov/spblas/
http://lapackpp.sourceforge.net/
http://www.cvmlib.com/
http://sourceforge.net/projects/lpp/
http://math-atlas.sourceforge.net/
http://www.netlib.org/lapack/
http://bytes.com/topic/c/answers/702569-blas-vs-cblas-c
http://www.netlib.org/lapack/#_standard_c_language_apis_for_lapack
http://www.osl.iu.edu/research/mtl/download.php3
http://scicomp.stackexchange.com/questions/351/recommendations-for-a-usable-fast-c-matrix-library

http://goog-perftools.sourceforge.net/doc/tcmalloc.html