This spilts out BufferDeallocationInternals.md, since buffer
deallocation is not part of bufferization per se.
Differential Revision: https://reviews.llvm.org/D94351
Added documentation about the bufferization features.
Furthermore, the usage of pre- and post-processing is described.
This also includes information about optimization functionalities.
Differential Revision: https://reviews.llvm.org/D90675