The user provides a comma-separated list of valid mouse actions
that will be performed one after another when a notification is
clicked. If any one of the provided actions is invalid, the value
reverts to its default state.
This adds the option `content_alignment`, which allows the user to set
the vertical alignment of the notification's content (i.e. icon and
text) to either top (`CONTENT_TOP`), center (`CONTENT_CENTER`, default),
or bottom (`CONTENT_BOT`). The default preserves current behaviour,
while the other options fulfill #486.
Changes all string parsers to have a the almost same interface while
also having a proper return value, which indicates success of the
parsing process.
It's hard to trace back, which methods in option parser require freeing
the result and which prohibit it. Marking all non-freeable values as
const lets this problem solve the compiler.
* Don't mix pragma guards and include guards, prefer classic include
guards since apparently pragma guards are not a standard yet.
* Use the DUNST_FILE_H naming convention for all include guards.
