* Add Dockerfile

* add KLAUS_VERSION build arg

Instead of returning an error 500 when a repository is invalid, keep
track of invalid repositories and display them in the repository list
with an error message.

Refs #238

Refs #238

3.7 is not available for trusty.

* When finding last update, ignore refs that point at missing objects.

* Don't break when sorting refs where some refs point at non-existing
objects.

Try a bit harder to come up with sensible names for tarballs and prefixes in tarballs.

table and img should look the same in index view and blobview

If readme files contain markup, they weren't displayed correctly in the
index view (no padding, no grey box).

The fix contains two changes:
- Use `force_unicode` on the readme's filename
- use the CSS properties for both blobview and non-blobview

use https for screenshot URLs

Properly keep track of exception so it can be reraised in force_unicode.

Recognize more Markdown file extensions for READMEs.

Ship klaus.1 manpage.

Put files in a tarball in a subdirectory.

Fixes #204

Set report_level to an integer.