New "flags" option in the [markdown] section to customize
Misaka's Markdown HTML rendering.
By default, no flags are set.
```
[markup]
flags = skip-html, escape, hard-wrap
```
Update CHANGES.rst and add the section to the sample
isso.conf and isso-dev.conf
"nofollow" is a deterrent for spammers: they cannot put links and hope
to increase their SEO when all these links have the nofollow
relationship.
"noopener" is a security for links opening a new window. They ensure
the target cannot control us.
Fix#373
* use a single default configuration, share/isso.conf
* try to use config.new in some tests which are decoupled
A few tests now depend on `isso.dist` to show that they (or the used
objects) have too much dependencies and need to be rewritten.
Jelmer Vernooij