semilinear: short-circut + and * for 0 and 1 elements
remove VarPtr typedef and improve the number of included headers
matrix: minor performance improvements in recursive_star
general cleanup
semilinear_set: don't use GcdDivider by default
semilinear_util: minor refactoring
matrix: import missing file...
Merge pull request #28 from michalt/semilinear

A few minor improvements