limit generated C preprocessor tokens to alphabet
limit generated C preprocessor tokens to alphabet

closes #407

The mangling strategy replaces bytes outside the alphabet
with "_xx_" where xx is the hex code of the byte.

zig-lang/zig,raulgrell/zig,raulgrell/zig,Dimenus/zig,andrewrk/zig,Dimenus/zig,zig-lang/zig,andrewrk/zig,Dimenus/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig