GFM parser: option to disable typographic symbol conversion

[kolyshkin]

With GFM, we want to be as close as possible to GitHub Flavored Markdown. In particular, GitHub does not replace -- with en-dash, --- with em-dash et cetera, and doing this not only breaks HTML rendering (resulting in, say, –option instead of --option), but also makes header IDs incompatible with those generated by GitHub. So, let's turn automatic typographic symbol conversion by default, and add an option to enable it back.

I have checked that this change makes header IDs the same as they are in GitHub.

For more details on the issue and examples, see #459

Signed-off-by: Kir Kolyshkin kolyshkin@gmail.com

[gettalong]

Thanks for your pull request!

Some comments:

• Please use the "gfm_quirks" configuration option instead of introducing a new one.
• The default value should not change, i.e. this quirk should not automatically applied.

[kolyshkin]

• Please use the "gfm_quirks" configuration option instead of introducing a new one.
• The default value should not change, i.e. this quirk should not automatically applied.

Done. I have two concerns though:

1. It looks like the value of gfm_quirks is not validated. Is it intentional (i.e. non-recognized options are silently ignored)? To my mind, it would make sense to have at least a warning printed, to figure out a typo or, say, an old version of parser where a specific option is not recognized.

2. If this option/quirk is not enabled by default, we still have those two problems that I described in the [GFM] wrong ID generation for headers containing -- #459. Isn't it your intention to make GFM parser as compatible with GFM as possible?

[gettalong]

Thanks for the changes! As for your concerns:

1. Yes, this is intentional so that custom parsers/converter can reuse the option.

2. Full compatibility with GFM will not be possible, at first because there was no spec and now because it is based on CommonMark. Therefore having this as option is preferable.

[gettalong]

I have cherry-picked your commit - the changes will be in the next release.