All conversions are performed as if in the "C" locale but without actually
changing locale.
This is a wrapper around printf/sscanf for int types which aren't affected by
locale and uses glib functions g_ascii_strtod and g_ascii_dtostr for
float/double types.
My first attempt at this used std::stringstream and
ios::imbue(std::locale::classic()) as it should be thread safe, but testing
shows it is not for gcc/mingw-w64 on Windows, and possibly also some versions
of macOS/OS X.
Use "yes" and "no" when converting a boolean in PBD::string_to<bool> as this
seems to be the convention used throughout libardour which will allow using
string_to<bool> in those cases.
Add accepted bool string values from PBD::string_is_affirmative to
PBD::string_to<bool>
Mark strings in pbd/string_convert.cc as not for translation
Add u/int16_t string conversions to pbd/string_convert.h and tests
Add DEBUG_TRACE output on conversion errors
Add int8_t/uint8_t conversions(using int16/uint16 types) to string_convert.h
Add support for converting an infinity expression to/from string
Follows the C99/C11 standard for strtof/strtod where subject sequence is an
optional plus or minus sign then INF or INFINITY, ignoring case.
