Renames all classes to PascalCase

It also renames BufferExt to bufferutils to adhere to the project idiom
that non-instantiable classes are inherently utility classes and
therefore adhere to lowercase.

ECKey and ECPubKey have also been seperated at the module level.
Script: remove redundant opcode.map access
opcode: less redundant indentation
ECKey/ECPubKey: seperates tests
bufferutils: correct test name