Added implementation of typevar_dim_pow
Added typevar_dim_pow_type.hpp and typevar_dim_pow_type.cpp
Remove the match/substitute implementation, update strided -> fixed
Rename typevar_dim_pow to pow_dimsym ("power dimension symbol")
Rename fixed_sym_dim to fixed_dimsym matching pow_dimsym
Implement pattern matching for the pow_dimsym type
Implement typevar substitution for the pow_dimsym type
Make the typevar map passed to substitute be const
Merge pull request #150 from mwiebe/type_dim_pow

Implements the pow_dimsym dimensional power type