Fixes #307 - Reviewed PayloadEscapeCharacter test set.

- Using EXPECT_ rather than ASSERT_ where possible, to provide more
  data regarding failure.

- ASSERT-ing buffer boundaries to prevent segfaults

- Adjusted some expected strings ( "&amp;" gets translated to "&",
  so we should be expecting that in place of "&amp;" )

- Adjusted formatting so that lines mostly wrap at 80 columns.
  Also adjusted comment style in a number of places.

- s/outsidetag/outside tag/ in plescapecharacter_unittest.cpp comments