Django-ca

- Add links for downloading the certificate in PEM/ASN format in the admin interface.
- Add an extra chapter in documentation on how to create intermediate CAs.
- Correctly set the issuer field when generating intermediate CAs.
- `fab init_demo` now actually creates an intermediate CA.
- Fix help text for the `--parent` parameter for``manage.py init_ca`

- django-ca now provides a complete OCSP responder.
- Various tests are now run with a pre-computed CA, making tests much faster and output more predictable.
- Update lots of documentation.

- The subject given in the `manage.py init_ca` and `manage.py sign_cert` is now given in the
same form that is frequently used by OpenSSL, "/C=AT/L=...".
- On the command line, both CAs and certificates can now be named either by their CommonName or
with their serial. The serial can be given with only the first few letters as long as it's
unique, as it is matched as long as the serial starts with the given serial.
- Expiry time of CRLs can now be specified in seconds. `manage.py dump_crl` now uses the
`--expires` instead of the old `--days` parameter.
- The admin interface now accounts for cases where some or all CAs are not useable because the
private key is not accessable. Such a scenario might occur if the private keys are hosted on a
different machine.
- The app now provides a generic view to generate CRLs. See [Use generic view to host a CRL](http://django-ca.readthedocs.io/en/stable/crl.html#use-generic-view-to-host-a-crl) for more information.
- Fix the display of the default value of the --ca args.
- Move this ChangeLog from a top-level .md file [here](http://django-ca.readthedocs.io/en/stable/changelog.html).
- Fix shell example when issueing certificates.