Update gitignore.
Add argument names to function prototypes.

In yet another shocking instance of my ever-capricious opinions, having
the names in the prototypes is useful (in the absence of proper
documentation) for hinting at the argument's purpose.
Modify set* function to accept a length argument.

C strlen is of linear complexity and the client library will almost
certainly know the length of the line already, so it's dumb to waste
time recalculating it.

Passing a length of 0 will make the functions use strlen to find the
length of the string.
Aegisub example: make version check less strict.
Aegisub example: fix some comment grammar.
Add C++ example.
Add MSVS13 project files.

Thanks to @line0 for creating the original solution that I based these
on. They are probably not perfect, but they seem to work.