V6.0 syntax update

[iAdramelk]

DO NOT MERGE

PR to show and discuss syntax and remark changes. We can still change syntax to something else having with below restrictions in mind.

First commit:

• Changed variables syntax: {{variable}}, (=variable=). (Had to select syntax without <>, {} and [] to prevent conflicts with existing syntaxes).
• Changed include syntax from {! CHANGELOG.mdx !} to (! CHANGELOG.mdx !) same reasons as above.
• Removed {% raw %} and {% endraw %} syntax.

Second commit:

• Updated remark parser and rerun markdown-fix task. New parser reeeeally like to escape symbols that can have double meaning now. Can revert it if we are ok with fixing errors manually instead of automated fixing.