Changed parser's handling of indents (scalars now valid after indents).

In other words, the following is now valid:

    a
      "foo"

Indent lexer tokens are now inserted after colons, as well. This should fix JSON parsing once and for all, though more tests will be needed to confirm...
Fixed line numbers in error messages.

Line numbers had been off by one.
Added lexer token output mode to command-line app.
Fixed incorrect ordering of outdents and commas.
Added several new unit tests.
Fixed block comments.

As far as I can tell, they didn't work at all before.