v1.2.0 - Rolled Repetition

Major improvements:

• Worked around a PyCharm autocomplete bug triggered by having """ in __doc__ strings.
• stim.Circuit no longer unrolls REPEAT blocks.
• stim.Circuit.__mul__ now wraps the circuit into a REPEAT block.

Minor improvements:

• Shorter stim.Circuit.__repr__
• Compiled samplers now have an eval-able __repr__.
• stimcirq no longer forces a specific version of cirq as a requirement.

Dev improvements:

• Split python and dev documentation into a separate README.
• Refactored underlying code to support streaming circuits with results too large to store in memory (not yet exposed as python bindings).