Add: Optional implementation of std::optional for pre-C++17 compilers.

Sourced from https://github.com/akrzemi1/Optional, Boost Software License, Version 1.0.

Change: Limit in-editor warnings in VS 2019

The AllRules ruleset causes the VS 2019 editor to litter warning squiggles all over the place, about things that would never be fixed. Limit it to the smallest ruleset available. Warnings shown now mainly concern potential arithmetic overflows.

Add: [Win32] GDI engine for font glyph rendering as a replacement for including FreeType.

Building with FreeType is still possible and will take precedence over the GDI renderer, but
the project files don't include FreeType anymore by default. Combining GDI rendering with ICU
text layout is untested.

Codechange: liblzma is called liblzma, how ever strange that might be

It is the only library we use that calls itself with 'lib' in the
name. This might be confusing, but with the arrival of cmake a lot
of these things are automated. And detection will find 'liblzma',
not 'lzma', like with 'lzo', 'zlib', ..