Document trashcan

@cython.trashcan directive to enable the Python trashcan for deallocations

Optimise internal fallback method call to ".__await__()" in Py3.7+ by directly unpacking the method instance.

Closes #2850.

Fix early binding example.
Closes GH-2848.

Closes #1470.

Closes GH-2845.

GCC diagnostic pragmas were introduced in GCC 4.6, so augment the GCC
compiler check with a version check to avoid compilation errors with GCC
< 4.6.

Avoid GCC diagnostic pragma if GCC < 4.6

GCC diagnostic pragmas were introduced in GCC 4.6, so augment the GCC
compiler check with a version check to avoid compilation errors with GCC
< 4.6.

REF: make Utils dependency-free by moving search_include_directories

REF: Move CompilationOptions and default_options to Options

update imports
remove Options.create_context in favor of Context.from_options

Avoid "__name__" hack in "Method" scanner action class and replace it with a simple "__repr__()" implementation.

Make the "Method" scanner action a direct feature of the embedded Plex, instead of hacking it back into the Lexicon with a stray import.
See GH-2831.

Resolve flake8 findings in Cython.Utils.

Closes #2802.

Remove unused code, mostly from Plex.

Misc. typo fixes

Found via `codespell -q 3 -L uint,sinc,nd,byteorder,delimeter,delimeters,te,iff,splitted,highlightning,tripple,varius,includee,ist,ue,ba,defin,amin,ith,creat,minimise,crasher`