Fix PGN reading and writing

[MarkZH]

Current code reads and writes PGNs line-by-line. The spec does not have this requirement and allows for comments and moves during the same ply to occur over more than one line (especially in export format).

Reading

• [x] Do not assume that a move text (number, SAN, commentary, variations, etc.) cannot span more than one line. Fix: read the entire game (stopping at the first blank line) and gather it into one string with no line breaks before parsing. <-- 10bd5eec446be6aeec14ce36ce10aaec776e6b6e

Note on above, it was simpler to change the parsing to go word-by-word or character-by-character.

Writing (export format)

• [x] Move numbers for black are only printed if there is commentary for the white move. --> ad88547f981f0f98ab39c499edce3925c9de15f4
• [x] Word wrap to 80 characters. --> 6ae197ca82c2b2a76e199a6f27733f7335af8f8a