STL containers, Less Submodules, improvements

There's a lot of new fixes and features in this release, which also comes with a wave of new documentation to describe everything.

• Container documentation is now available to help people use containers better.
• do_string and other more friendly functions are now present.
• Error handling tips and tricks! This one should help a lot of people.
• Documentation for read-only tables in online and should help guide people.
• Usertype has a top-level category in the documentation for lots of goodness.
• Specialization traits now have a top-level category to describe their usefulness. (A bug with the is_container trait was also fixed: thanks crazyc and MAME!)
• We no longer submodule the Optional header, since it has changes so drastic from the initial implementation we changed. It is now included in the rest and nobody has to recursively initialize submodules anymore to pull from the Git repository.