We've just checked whether a sub-path started with "name/", but that
changes behavior whether the property name has a trailing '/' or not.
Using a helper function to split of path components avoids this problem.
Allows retrieving properties by their native values (or something close
to it), rather than having to go through string conversion. The caller
could actually just copy the value itself and then use the m_option
functions to convert it to mpv_node, but maybe it's more flexible this
way.
This adds a mechanism for easier export of sub-properties. The following
commits will make use of it to export fine grained information about
certain things. The sub-property mechanism reduces the amount of code
needed to export a data value to 1 line.
Since m_option.h and options.h are extremely often included, a lot of
files have to be changed.
Moving path.c/h to options/ is a bit questionable, but since this is
mainly about access to config files (which are also handled in
options/), it's probably ok.
