Config: Parse from command line options on top of config file

Any options that are not arrays (ie. RTP paths) specified
as command line options will override entries in mkxp.conf.

The syntax is: --<option>=<value>
Spacing
Use stdint types
FileSystem: Trim redundant error message on ENOENT

MRI adds the "No such file or directory - " itself;
I guess we can just emulate this behavior everywhere else.
FileSystem: Fix path cache for mounted zip archives
Merge branch 'dev'