Add autoEscape option, |safe filter and |e,|htmlEscape filters

[iffy]

Fixes #94

Let me know what you think of this approach.

[enthus1ast]

Thank you @iffy this looks really good!
I think supporting html only for the moment is good enough.

Could you:

• inc the version to 0.11.0
• add one entry in the readme's changelog (under done)
• write a short entry in the readme that describes the feature

then i'll merge it

[iffy]

Thank you @iffy this looks really good! I think supporting html only for the moment is good enough.

Sounds good. Because of how you've made this lib, it would be really easy to support other escaping modes (besides HTML) by choosing a different proc for nwtStrProc. It was a pleasant surprise to see how nice this was to add. Kudos!

Could you:
* inc the version to 0.11.0
* add one entry in the readme's changelog (under done)
* write a short entry in the readme that describes the feature

All done! Let me know if more changes are needed.

[heuer]

Wouldn't it be sufficient to utilize escape proc of std/xmltree instead of implementing htmlEscape?
See https://nim-lang.org/docs/xmltree.html#escape%2Cstring