Automatic code-generation and definition strings lengths from 1 to 25, done through the unrolling the templated functor.
Commented out the function str_grp/T_str_grp that is not currently in use.
To speed up the compilation, better to use a lot of translation units and to scatter functions across them. It also solve the problem of the big size of the object files.
Merge pull request #20 from AlexeyAB/fix_static_string

Automatic code-generation and definition strings lengths from 1 to 25.