Refine and combine the Syntax for Plugins and Constants, i.e. {{...}}

[Piiit]

Create a better definition of these notation.
This includes:

• remove ~~plugin:category~~ syntax
• new syntax = {{command|parameter1|p.2|...|p.n}}

Refactor:

• Constants are no a simple plugin, not a separate token anymore: new syntax = {{plugin.method}}, ex. {{wiki.id}}
• Variables (is a plugin from now onwards): new syntax = {{var|variable-name=value}} or for arrays {{var|variable-name=[a1,a2,a3]}} to set them, and {{var|variable-name}} for output
• Plugins: new syntax = {{cmd|cmd-name|parameter 1|...|parameter n}}

This are section patterns, that is, newlines are allowed within {{...}}

[Piiit]

TODO: varvalues > array syntax for values
TODO: varnames > error handling for illegal variable names (define clear regexp for varnames
TODO: varvalues > multiline value support