option
This commit refactors string_stream and string_streamx into a common
basic_string_stream template class. When the EXT template == true, the
string_streamx formatting options are enabled, they default to disabled.
These options are enabled at compile time, and do not affect performance
when they are disabled. By implementing the two streams in this manner,
duplicated code is removed.
This commit also adds the ENDL template paramter. When ENDL is set to
zero, no endline character is printed when piping mtl::endl. Otherwise,
the character is printed. Defaults to '\n'. This allows logging on the
GBA to handle mtl::endl correctly and not print two newlines on the MGBA
emulator.
