Add a match for the combination of OpeningBracket and Pard in the parse_header method

[zyk-mjzs]

html-to-rtf generated RTF can be previewed on Mac，but error with MalformedPainterStack

{\rtf1\ansi\deff0{\fonttbl {\f0\fnil\fcharset0 Calibri;}{\f1\fnil\fcharset2 Symbol;}}{\colortbl ;}{\pard \u21435  \sb70\par}}

I add a match for the combination of OpeningBracket and Pard in the parse_header method, and add a test named parse_opening_bracket_and_pard

[d0rianb]

The issue is deeper than just for the \pard. To properly fix this, we should add a check for every "break" word that made the parser exit the header parsing (plain, pard, par, etc) to see if it's preceeded by an opening bracket (since it's allowed by the RTF specification.
Identifiying the end of the header is a problem that I have since the beginning of the project and I'm considering merging the parse_header method with the parse one.

[zyk-mjzs]

我认为这样可行

The issue is deeper than just for the \pard. To properly fix this, we should add a check for every "break" word that made the parser exit the header parsing (plain, pard, par, etc) to see if it's preceeded by an opening bracket (since it's allowed by the RTF specification. Identifiying the end of the header is a problem that I have since the beginning of the project and I'm considering merging the parse_header method with the parse one.

I think this is feasible

[d0rianb]

This is a temporary solution. I will merge it into master and continue working on the rework of parse_header on another branch.