* - added basic_string allocator support to BasicStringRef, BasicCStringRef, BasicWriter::str, StringBuffer and BasicStringWriter

* - removed templated str() and to_string() function
- code style fixes

Fixes #413.

This adds thread-safe (at least on platforms that provide necessary extensions) replacement functions for std::localtime and std::gmtime. Alternatively they could be placed in a new source file time.cc, but time.h seems so empty right now...

Remove unnecessary "fmt/" prefix which should be maintained with additional include_directories() in each project. (#397)

Document use of format_arg for user-defined type

Introduced NamedArgWithType<Char, T> : NamedArg<Char>

Extend ArgLists to support serialization/deserialization in third-party components

Add FMT_OVERRIDE macro to allow specifying overriding functions

Fix compilation on Android.