stop tracking generated `./configure'
Typo
Correct symbol conflict with pow10 function
Correct #include directives

Add several standard library headers in f8types.hpp and f8utils.hpp;
use fix8/ prefix in <> includes in .cpp files
Remove extern "C" in modp_dtoa declaration

Since this is a C++ project anyway, it isn't useful to declare C linkage for a
single external function.