* Allow %s as generic format specifier in printf

Signed integers are formatted as %d
Unsigned integers are formatted as %u
Doubles are formatted as %f
Chars are formatted as %c
Void Pointers are formatted as %p

* Remove '%S' handling and use visitor for generic format strings

* Default for floating point is now "%g" rather than "%f"

* A custom FormatSpec type can be passed as a template argument to the ArgFormatter chain (#439)

* Corrected nested-name-specifier error

* Spec template argument defaulted to FormatSpec

* Forward declaration of FormatSpec

* Style

* Style (part 2)

* Style (part 3)

* - 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