Dmitry Voronin

Add SafeImageSpecField

2

Add SafeImageSpecField that will not raise exception if source file is absent.

If we use `-dev` as prepare version suffix we got endless raising suffix. We got after few bumps: ``` version='0.2.20.-dev.-dev.-dev' ```

I think it's not OK

If we don't specify version part neither by param neither config file, but specify vcs param, bumpr try to commit with no changes. I think it's good to set `part`...

I didn't find Changelog section in Configuration file description

If we use prepare version we got: ```console -> Bump version 0.2.20 -> Prepare version 0.2.20.dev ``` I'd like to have other. Bumped `patch` part and suffix after minus. ```console...

`disqus_developer` var is deprecated. We can remove `{% set_disqus_developer 1 %}` tag. There are additional `shortnames` for that goal. https://help.disqus.com/customer/portal/articles/1053796-best-practices-for-staging-development-and-preview-sites

Duplicate of #37 without file backup

In other case example from docs doesn't work http://django-disqus.readthedocs.org/en/latest/templatetags.html#set-disqus-identifier