Silicon v3

[EimaMei]

The next major Silicon version.

Requirements that need to be met

• Removal of si_initNS, SI_NS_CLASSES and SI_NS_FUNCTIONS along with their associated enums.
• Complete the documentation for each Cocoa and Silicon specific function.
• Add documentation for how to extend Silicon with new methods and properties (based on #11).
• Fix #19 and rework the function -> SEL system.
• Add one Metal example from the official Apple sample codebase (somewhat based on #11).
• Review pre-existing examples for any possible errors, mistakes or typos.
• Update CONTRIBUTING.MD to reflect the new changes in the library.
• Add more debug options for catching bugs (eg. using a string or a non-existent class for NSClass)
• Review every <class>_init... function and rewrite them to take a <class> argument.
• Have a section in the README.md about projects utilizing Silicon in practice.
• Rework the Makefile and reinstate the old way of how Silicon examples were compiled before (that being before the existence of the Silicon-h fork);
• Complete the TODOs from silicon.h

NOTE: The list of requirements for the update is sorted by oldest added items, not of importance.