Add a `disable_defaults` option to the config parser

This option is useful to force the parsing of a single configuration file,
for instance to be able to query a configuration value set in that file.
Add some features to fedmsg-config

 --query: retrieve the value of a given configuration key
 --disable-defaults: only print overridden configuration values
 --config-filename: only print the configuration for the given file
Merge pull request #222 from olasd/feature/query-config

Add some features to fedmsg-config
Avoid importing pkg_resources in fedmsg.meta

Not sure why, but till reported a related UserWarning here:
https://admin.fedoraproject.org/updates/fedmsg-0.7.5-1.fc19
Merge pull request #223 from fedora-infra/feature/avoid-pkg_resources

Avoid importing pkg_resources in fedmsg.meta
Add the possibility to fedmsg-tail to only return the topics of the messages
When printing only the topics, no need to clean the credentials
Merge pull request #224 from fedora-infra/feature/tail_topics

Add the possibility to fedmsg-tail to only return the topics of the messages
Handle dates too.

fedmsg.encoding can handle encoding datetime objects and time structs.

This allows it to handle datetime.date objects too.
Merge pull request #225 from fedora-infra/feature/handle-dates-too

Handle dates too.
Add the --query argument to fedmsg-tail
0.7.6
Merge branch 'release/0.7.6' into develop
Add support for fedmsg-taill --query to return multiple items provided as a comma separated list
Small pep8 fix to make pep8.me happy
Fix the --query to enable filtering for multiple, different elements in the messages
Handle dates too.

fedmsg.encoding can handle encoding datetime objects and time structs.

This allows it to handle datetime.date objects too.
0.7.6
Combine the dict_query from fedmsg-config and fedmsg-tail into the same function.
Merge pull request #227 from fedora-infra/feature/fedmsg-tail-query-combined

Feature/fedmsg tail query combined