Release 0.2.1

This is a minor release with some fixes and cleanups.

We now distribute all the demos in the tarball and there was some
fixes to make them work on more distributions and with different
versions of python.

There was an issue with mkdir when running bubblewrap on an NFS
filesystem that has been fixed, so flatpak now works on NFS shares.

Some leaks have been fixed, including a file descriptor leak.

bubblewrap now builds on systems without PR_CAP_AMBIENT.

```
Alexander Larsson (2):
      Don't rely on mkdir returning EEXISTS (fixing NFS)
      Release 0.2.1

Marcos Paulo de Souza (2):
      Remove O_RDONLY flag when O_PATH is used
      README.md: Remove double dots

Mickaël Salaün (1):
      bubblewrap: Do not leak FDs dedicated to setup_newroot

Philip Withnall (2):
      tests: Correct number of tests in test-run.sh
      bwrap: Second attempt at fixing an argv handling leak

Simon McVittie (5):
      build: Include various interesting files in tarballs
      Skip prctl(PR_CAP_AMBIENT) if PR_CAP_AMBIENT isn't defined
      userns-block-fd: Search $PATH for python
      userns-block-fd: Search the PATH for bwrap
      userns-block-fd: Add support for Python 3
```

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