Fix K.match() on regex filter

[XavierBrassoud]

Issue

Prevent the regex filter from returning an object instead of a boolean
re.match return an object if match, None else

Demonstration

In this case, K.match() return a re.match() object instead of a boolean:

assert K(['=~', 'f', '^hi$']).match({'f': 'hi'}) == True # Fail.

Tests also broken. False positive here, object is not None so you got True:

def test_basic_regex_true(self):
    self.assertTrue(K(['=~', 'f', '^hi$']).match({'f': 'hi'})) # Success => False positive!
    self.assertIs(K(['=~', 'f', '^hi$']).match({'f': 'hi'}), True) # Fail as expected before the fix

This fix include a little class helper that shortcuts self.assertIs(exp, true) to self.assertIsTrue(exp) following your conventions. Tests are also updated with assertions helpers that follows Python AssertIs recommendations for booleans strict checking.

Fix

Changed this line:

'=~': lambda match_str, regex: regex.match(match_str) if match_str is not None else False,

By this line:

'=~': lambda match_str, regex: regex.match(match_str) is not None if match_str is not None else False,

is not None explicit convert re.match() to boolean as K.match() should work.

[somewes]

thanks for this pr @XavierBrassoud sorry i didn't see it sooner. i can circle back around to this and get it merged in