[lldb][docs] Fix reference warnings in python-reference.rst

References with a single '`' around them are interpreted as references instead
of text with monospaced font since the introduction of the new Python API
generator. This meant that all the single-quoted code in this document that
doesn't reference any Python class was throwing sphinx errors. This just adds
the neede extra ` around this code and fixed up the legitimate typos
(e.g. `SBframe` -> `SBFrame`).