Add basic outline of Forth and explaination of simple concepts.
[bash/fr] A couple formatting/phrasing issues fixed

Thanks to @vendethiel’s feedback on #824.
Merge pull request #858 from bfontaine/bash/fr-fixes

[bash/fr] A couple formatting/phrasing issues fixed
Finished conditionals section for now.
Add outline of loops.
yaml-fr fixes
yaml-fr fixes
Merge pull request #859 from AndreiCurelaru/master

yaml-fr fixes
Finished outline of Variables and Memory. Must be more vague, this is a whirlwind tour!
Be more brief!
Refactor section Stack Manipulation.
Improve section Advanced Stack Manipulation's examples.
Merge remote-tracking branch 'upstream/master'