Fixed - was not working for variables in last line of heredoc.

It seems that heredoc() method excludes terminator line, so no need to pop()
https://metacpan.org/pod/PPI::Token::HereDoc#heredoc

added test for the bug, also added additional test to extract_variables (just
to make sure our regexp deals with newlines right)
(GH-14) Add test for the double-quoted heredocs.
(GH-14) Fix inconsistency in PPI::Token::HereDoc->heredoc().

Due to a bug in PPI::Token::Heredoc, $token->heredoc() does not include the
terminator line when the terminator is a simple bareword, but it includes the
terminator line in the other cases (single/double quoted , commands, escaped).

I wrote a patch to resolve this in PPI (see
https://github.com/adamkennedy/PPI/pull/71), but in the meantime this addresses
the inconsistency.
this typo prevented the test from working
Revert "(GH-14) Fix inconsistency in PPI::Token::HereDoc->heredoc()."

This reverts commit 49b2c9b20be10f91c46c3ace145fc6a4a1b15b25.

Upon further investigation, I found that the issue is not in PPI but in the
test cases in this module. I will commit a fix for those separately, but I am
reverting the PPI workaround and I have cancelled the PPI pull request
accordingly.
(GH-14) Fixed here-doc terminators.

The closing terminator should not include quotes/backticks/etc, or it will not
be detected as a valid closing terminator and be included in the heredoc()
output instead, which is the real cause of the issues we've seen in GH-14.
Merge pull request #16 from regru/typo_in_test_file

(GH-16) Missing "name" keyword prevented a test from working.
Merge branch 'master' into gh13_function_calls