parser: extends grammar to support annotations

Signed-off-by: Jean Privat <jean@pryen.org>
nitc: globally skip annotation nodes

Signed-off-by: Jean Privat <jean@pryen.org>
rta: do not enter in annotations
tests: add syntax_annotations

Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'annotations'

Conflicts:
	src/parser/lexer.nit
	src/parser/tables_nit.c
phase: add `Phase#process_annotated_node`

Signed-off-by: Jean Privat <jean@pryen.org>
parser_util: add `ANode#collect_annotations_by_name`

Signed-off-by: Jean Privat <jean@pryen.org>
modelbuilder: generalize mpropdef to APropdef

and create a virtual type MPROPDEF to link AST and model hierarchies

Signed-off-by: Jean Privat <jean@pryen.org>
phase: add new module cached.nit

Signed-off-by: Jean Privat <jean@pryen.org>