Fix COUNT(DISTINCT col) without GROUP BY

Assign a value for the key used to enforce uniqueness for DISTINCT
columns in do_calc(). This ensures the logic to skip seen column values
works correctly, especially in the absence of GROUP BY.
Fix space parsing error with '>=' and '<='

Ensure that the regular expression to insert space around operators
doesn't match the '=' in '<=' or '>='.
update meta-spec to v2 and add more author tests
add MANIFEST to the .gitignore list
fake release dates of 1.18_02 and 1.21_7

To be clear: I want the failing date-time format test for Changes to avoid
releases with broken dates. The price of an unknown date being replaced
by an approximated one in a suitable range sounds fair to me.
be more strict in use

* add q[use strict; use warnings FATAL => "all";] to every package
* favor q[use ... ()] over require
apply reworked Perl::Tidy rules
Merge branch 'fix-distinct' of https://github.com/grantisu/SQL-Statement into grantisu-fix-distinct

Conflicts:
	lib/SQL/Parser.pm
	lib/SQL/Statement.pm
Tidy patches after merge