Assign scope selector for Help command

To make it show up in the "Select Bundle Item" explorer only when a
Turtle document is active
[tmp] Temporary disable RDF/RDFS QName completions
Update README

+ Add roadmap
[tmp][tryout] Introduce Autocomplete command action
[demo] Add demo documents

+ grammar-demo.ttl used for grammar testing
+ visualize-demo.ttl used for testing Graphviz visualization
[snippet] Introduce directive snippets

Snippets for @base and @prefix directives
[autocomplete] Introduce completions

+ Bultin XML Schema datatypes
+ Some language tags
+ Some literal datatype foo
[grammar] Update language grammar

+ Allow IRIs are subject, predicate or object
+ Support base directive
+ Support single/double/triple quotated strings
+ Try to add meta scope to make autocomplete for literal datatypes work
[autocomplete] Update completions for literal datatypes and language tags
Turtle statements are be collapseable and indented properly
[grammar] Update language grammar

+ support for object lists
+ @base directive
+ support full IRIs (not only URIrefs) as SPOs
+ multiline literals
+ fix support for autocompletion of literal datatypes/langtags
Rearrange menu items
Add .gitignore files
[autocomplete] Complete rework of autocomplete for prefixes and resources

+ for literal datatypes (for now only XSD)
+ for literal language tags
+ for prefixes and their according IRI/ref (automagically fed by
prefix.cc)
+ for all prefixed resource names (automagically from vocab/onto URI
when machine readable representation exists)
Rearrange menu items

+ "Help" was renamed to "About"
+ Change menu item order
Only @prefix directives are listed in symbol list
Introduce automatic in-place documentation of current resource
[grammar] Updated language grammar
Add list icons

Seems like support for list item icons is broken in TM2
Update .gitignore

+ Remove grammar test docs