Freestanding Support, Bugfixes & Optimizations

Fix naming in README

Changed "Feestanding" to "Freestanding"

Added optional & variant support

Added optional, variant support, re-formatting of code, and minor

fixes.

v0.3

Fixed readme typo.

v0.2

Adopted shared_timed_mutex in C++14, due to the lack of shared_mutex.

v0.1

Compilation fixed for some versions of visual studio.