Remove no-longer-used header variable in ass parser
Pass nullptr for the codepage for ass_read_memory

Passing a codepage makes libass convert to UTF-8 even if it's already
UTF-8.
Make missing boost libraries a configure error. Closes #1707.
Update libass
Return a rgba string for coloralpha lua controls
Cut the opacity of the vector clip tool's lines a bit
Adjust the appears of the vector clip control handles

Make them significantly smaller to cover less of the video and fiddle
with the appearance to hopefully make them still visible enough.
Add Release-MinDep solution configuration
Use splice rather than swaps to pop the undo stack
Make BaseGrid::UpdateMaps far less slow
Redesign the undo stack

Store the data in vectors rather than AssFiles since even an intrusive
linked list has comically high memory overhead. Cuts memory usage of a
full undo stack with 15k lines by 65 MB for 32-bit and 130 MB for
64-bit. Also roughly halves how long it takes to copy the file for the
undo stack, and makes undo/redo a bit faster.
Store selection and active line in undo info and restore them on undo
Remove the added/removed items arguments from the selection changed signal

They're only used by one thing (the drag visual tool), so calculating
them is pointless overhead most of the time, and it simplifies the
visual tool code much less than it complicates the grid code.
Sort the actor and effect fields. Closes #1715.
Match the parser's section order when constructing files for undo
Update to moonscript 0.2.5
Flush the clipboard on exit

Apparently flushing immediately after setting the clipboard sometimes
doesn't work.
Eliminate some duplicated exception handling code
Split AssFile into separate lists for each section
Remove some cruft from TextFileReader