very raw implementation of cross-reference integrity check
bugfixes + project check diff for 2 arbitrary revisions
doc pluging for integrity check report
adding constants and static class properties
checks for static/instance access + visibility
Merge branch 'master' into project-check

Conflicts:
	XRef.class.php
	lib/interfaces.php
using new parser for project-check
fixing error found by the lint on itself
allow to inherit constants from interfaces/traits
allow abstract classes to use methods inherited from interfaces
warning for missed classes/base classes
minor fixes
cleaning code; new interface class - XRef_IFileProvider
Merge remote-tracking branch 'origin/master' into project-check

Conflicts:
	XRef.class.php
	lib/interfaces.php
separating project lint and project database; work in progress
cmd-line options: allow only-short or only-long options
cmd-line options: better error handling
config file: looking it up in current dir
file providers: refactoring
project check: new interface XRef_IProjectLintPlugin