mission.msg remaining tasks

[ExpHP]

I stopped work rather abruptly on mission.msg to try and work on ECL before the TH18 release. Some tasks I left:

• Tests of TH095 and TH125 mission.msg decompilation.
  • Include tests with const variables!
• Test of the error message when trumsg -g 095 is used without --mission
• TH125 entries have 6 strings; three lines of text followed by three furigana strings. It'd be nice to put the furigana strings up next to the furigana positions, like [[12, 0], "hello"].