CLN: make resolvers attribute of Scope object a tuple

We don't want modification of resolvers tuple after construction of the Scope
object.
DOC: add doc examples for not and for a more complex query
TST/DOC: add complex query test and add more thorough doc example for logical negation
ENH: added interpretation of 'in' in pytables Term syntax

which is syntactically equivalent of '='
ENH: allow parsing of datetimes
ENH: give visitors their own term and const type class vars
TST: smoke test for datetimes
ER: add NameResolutionError, a NameError subclass
CLN/ENH: add syntax check before name resolution attempt
CLN: move query to its own test class and add scope tests
ENH: ensure that resolvers do not overlap with current scope