Fixed implementation for parse_{start,end}_date
Do not return 1 in case the variable is nil, we must handle this outside
Rewrote #search_in? Implementation
Added tags/categories printing

Added helper methods to get tags and categories out of an entry and
printing this metadata with the cat command
Merge pull request #64 from matthiasbeyer/add-metadata_to_cat_command

Add the ability to print tags/categories when using --cat
Merge pull request #63 from matthiasbeyer/implement-limit_range_command

Implement the Command for limiting by range
Fix: Use empty array if there are no categories in the hash
Fixed Command.is_command? check, as prefixes get checked by Regexp
The LimitTagCommand classes have no arguments, they are the arguments to themselves
Ensure we iterate over something non-nil in here
The TagCommand shouldnt work with +<tag>
We must pass the callstring to the Command instance for the TagCommand classes
Added some debugging output
We must check against the callstring here, not the arguments (as we have no args)
If we have a prefix as identifier, we use this one instead as key string
Added help strings
This stuff can be protected in here
We must replace the appropriate identifier in here
Merge pull request #67 from matthiasbeyer/implement-limit_by_metadata

Implement the LimitMetadataCommand classes
Added test for SymbolHash class