#3 Re-implement song info guessing

[Anders Sandvig]

- Implement MediaFile::GuessFileInfo() using new RePat
C++ library.

[Jřrgen H. Seland]

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Completed, though not yet submitted.

[Jřrgen H. Seland]

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Rewritten to use the PCRE library. It's more robust and flexible
than the custom repat lib, albeit less user-friendly.
Some debugging of the actual regular expressions used remain.

[Jřrgen H. Seland]

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Technology implementation complete. Regular expression list
still needs some polishing.

[Jřrgen H. Seland]

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PCRE compilation now shows meaningful error messages rather
than crashing. Remaining points:
- debugging/adjustment of the default regexps
- documentation for the filename_formats.txt file

[Jřrgen H. Seland]

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PCRE compilation now shows meaningful error messages rather
than crashing. Remaining points:
- debugging/adjustment of the default regexps
- documentation for the filename_formats.txt file

[Anders Sandvig]

No longer relevant, I assume?

[Jřrgen H. Seland]

I have a much improved version of the PCRE-based thing in C# - we can use that if desired. I discovered it was pretty hard matching all those different filename formats with a list of regular expressions - we need some kind of live parsing support that runs in the background on a pre-loaded list of file names, otherwise it is too hard to see the results of regexp changes and reordering. Needs to be pretty fast to be useful on 20k song libraries.

[Anders Sandvig]

I am currently rewriting media library scanning to run in the background as a separate process (via mlscan.exe). If feasible, mlscan can do the guessing via a DLL based on the C# code. If not, the guessing could run as a separate process in the same way as mlscan, accessing the media library database directly.

[Anders Sandvig]

Moved to backlog for further consideration.