Changes the implementation of numbers parsing from std::atoi/f to
std::strtod/l. These support setting the optional end-of-string pointer
which are used to determine if a parsing was successful or not. This has
the nice side effect of *greatly* simplifying the logic, at the expense
of some C-style details.
Tests added to verify that the different edge cases are handled
properly.
8e4e9b15d8