This marginally increases memory use, but vastly speeds up pretty much
everything when a file has attachments (other than extracting the
attachments, but that's generally IO-bound anyway).
Use boost::filesystem::path for all paths, and std::string for all other
strings, converting to/from wxString as close to the actual uses of wx
as possible.
Where possible, replace the uses of non-UI wxWidgets functionality with
the additions to the standard library in C++11, or the equivalents in
boost.
Move the path token management logic to libaegisub (and rewrite it in
the process).
Add a basic thread pool based on asio and std::thread to libaegisub.
This touches nearly every file in the project and a nontrivial amount of
code had to be rewritten entirely, so there's probably a lot of broken
stuff.
Now that all the other junk is being dropped from the file, script info
lines are the only thing left which was a concrete AssEntry, and
AssEntry wasn't actually a very good way to store them.
Dealing with multiple instances of each section makes the code
significantly more complicated, and in most cases Aegisub doesn't
actually bother to handle it correctly.
Previously, Aegisub wrote its "Script generated by" lines without a
semicolon to mark them as comments. As a result, it prepended these
lines every time a script was loaded and then saved again. Fix.
Also fix a bug that caused the ASS parser to treat comments before
the [Script Info] section as non-blank lines, therefore inserting a
duplicate section header whenever such comments were present.
