Change Document Meta Format

[vkbo]

This PR changes the format of the meta data written to the top of document files.

The point of the change is to make the format easier to parse and extend. Currently, the single line is getting a bit information dense and there are a few pitfalls and limitations to parsing it. Especially since it contains user controlled data (the document label).

The new format changes the format to a label/value style where the first N characters can be checked, and the remainder of the line be treated as the value, regardless of content.

The previous format was:

%%~ 6a2d6d5f4f401:e7ded148d6e4a:7031beac91f75:NOVEL:CHAPTER:Chapter One

The new format is:

%%~name: Chapter One
%%~path: e7ded148d6e4a/6a2d6d5f4f401
%%~kind: NOVEL/CHAPTER

Any line starting with %%~ will not be loaded as text (although only the first 10 lines are considered). Also, any line that does start with those characters, but don't match any of the above keywords, like %%~name:, will be discarded.

As a bonus, the new format is also more human readable.