[RPC] Single-connection interface

[m-yac]

This PR adds a single-connection interface for the python Cryptol RPC bindings based on the existing synchronous, typed interface. Since the argo server's default setting is to only allow a single connection at a time, this interface is a better fit for the expected use case of these bindings. The existing interfaces, where multiple Connection objects can be created, still exist and are unchanged.

Compared to the synchronous interface, this change lets us get rid of the "c."s in front of every command. Compared to the old interface, this change also lets us get rid of the .result() calls and adds more types. For example, what was before:

c.call("f", x).result()   # type: Any
c.prove("prop").result()  # type: Any

is now:

call("f", x)   # type: CryptolValue
prove("prop")  # type: Union[Qed, Counterexample]

Link for comparing this interface to the old interface: 5a668a4...rpc/single-conn-interface (e.g. check out the test cases)

[atomb]

I think this looks really nice, and should make simple scripts less noisy. The one CI failure is, I believe, and issue with the CVC4 binaries we're using. I'm looking into fixing it separately.

[atomb]

Perhaps try rebasing/merging with master and see if CI succeeds now. I think it should.

[pnwamk]

This PR should probably bump the client version and document what is added briefly in the CHANGELOG.md file.

[m-yac]

This should be ready to merge, the RPC bits of the CI have passed.

The changes made in this latest batch of commits are:

• Update the synchronous and single-connection interfaces with timeout parameters
• Add a timeout property to the synchronous interface to match the timeout member field in the old interface
• Add get_default_timeout/set_default_timeout methods to all three interfaces (since the single-connection interface can't have a timeout member field or property)
• Update the changelog and bump the version number to 2.11.7

[m-yac]

The CI passed for the second most recent commit, and the most recent commit just fixes a typo in CHANGELOG.md - so I'm going to merge this