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.
Decouple it from the subtitles grid and do everything through the
project context instead.
Actually obey the "In Selection" option for things other than Replace
All.
Cut down on the amount of logic duplicated between Replace All and
normal find/replace.
Start searching from the current cursor position, rather than the last
found position.
