Treat backslash as normal char in TextElements

[stasm]

Fix #123.

[Pike]

The general idea is right. Also the tests are OK.

I think there's symmetry coming between { and } which I'd expect to be expressed differently than right now, but maybe I'm off.

The ebnf is rather confusing in its grouping and the comments, sadly. Can you shuffle and group/paragraph that to be more, well, grouped and paragraphed?

/* Double quote and backslash need to be escaped in string literals. */
special_quoted_char ::= "\""
                      | "\\"
text_char           ::= any_char - special_text_char
/* Indented text may not start with characters which mark its end. */
indented_char       ::= text_char - "}" - "[" - "*" - "."
special_escape      ::= "\\" special_quoted_char
unicode_escape      ::= "\\u" /[0-9a-fA-F]{4}/

is really hard to read right now, in particular as the comments earlier usually denote block comments. And here, the comments don't make any sense as block comments.