Post-release refinement of documentation
Move xtoa.inc so it can be found with standard include path
Share signed and unsigned implementations of xtoa

This should be safe since the data types have the same number of bits, and
signed/unsigned cast has no effect on the bit representation.
xtoa: add long long option
Improve handling of modulus operator

Avoid undefined behavior by making sure everything is unsigned; also use int
instead of char to avoid a TI compiler bug.
Improve CCS support
Move generated archive into lib subdirectory

This means we can use EMBTEXTF_ROOT to point to either a source root or an
installation root.
Refactor configuration options out of public interface

These cannot be modified by an application when the application is built;
they influence behavior only when the embtextf library is built.  Yes, it's
still ugly and I don't like it.
Remove conditional availability of llxtoa

All target toolchains support long long, which is part of C99 and can
reasonably be expected to be available in 2013 CE.
Update version and documentation for new release