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In particular:
1. Windows CR/LF weren't read properly (issue #11)
2. Scanning wasn't reading EOF properly
3. Documents may be empty (this was old, I think)
Also fixed some VS2008 warnings on /W4.

We were getting memory leaks (as told by the CRT detectors, which I also added), and there's really no reason (as long as we're careful) to use pointers there.

Combined the myriad ScannerExceptions and ParserExceptions to a single ParserException class that has a message and a line/column position in the file where the error occurred.

Fixed a bug in the last newline of a block folded scalar.

Moved the three scalar token scanning functions back to scantoken.cpp, so scanscalar.cpp now only has the main scalar scanning function.
Renamed ScanScalarInfo to ScanScalarParams.

Renamed the valid/possible tokens to a single variable status with enums valid, invalid, and unverified.

Moved the input stream, together with line/column info, into its own class, which allowed some other stuff just to pass the stream, and not have to be a member of Scanner.

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There's a bug (and question): should we test simple keys' validity BEFORE stuff or AFTER stuff?

Refactored some common whitespace-parsing code in scanning both scalars.
Implemented the flow collection tokens.

Split off the specific regular expressions, and the specialized token-scanning functions, into their own files.