v0.8.0

CHANGES:

Bug fixes and diagnostics:

• Don't GC imports with callbacks (@talex5, #210).

• Improve "Already resolved!" error message (@talex5, #209).
  Show the state of the promise we were trying to set, and what we tried to set it to.

• Reject attempts to send after disconnecting (@talex5, #208).

• Unix: don't leak FDs if Network.connect fails (@talex5, #206).
  Also, use Lwt to open connections so we don't block the whole process.

New functions:

• Add Sturdy_ref.with_cap and with_cap_exn convenience functions (@talex5, #207).
  Using the plain connect functions, it's easy to forget to release the live-ref at the end.

Build changes:

• capnp-rpc-mirage: adapt test to tcpip 5.0.0 API (@hannesm, #205).

• Upgrade to dune 2 (@talex5, #204).

• Switch tests to build in native code and use the test stanza (@avsm, #203).

Documentation:

• Show how to make a connection directly (@talex5, #202).
  The new test-bin/calc_direct.ml example shows how a parent process can
  spawn a child and communicate with it directly over a socketpair.