bring in Pod::Checker warning about =over without =back
whine when L<> starts or ends with whitespace

For example:

  L< Foo>
  L<Foo >

It leads to confusion.  For example, L<Foo> is a link to the module
Foo, but L< Foo> is a link to the section " Foo" in this document.

This check was in Pod::Checker.  In fact, Pod::Parser was resolving
things the *other* way!  It trimmed whitespace first!
issue a warning on raw | or / in L<text|link> text
tests for recently added warning

also a bit of framework for testing more warnings later
Merge pull request #48 from rjbs/master

New warnings from Pod::Checker.

Plus tests for whine.
Note new warnings thanks to @rjbs.
Add regression test for encoding behavior.

Broken in fc97ecd.
Prevent output of =encoding in most cases.

Add `keep_encoding_directive()` which is false by default, to prevent
formatters from emitting a document's `=encoding` directive in most cases.
That they emitted the encoding was a bug introduced in v3.26 (RT #84093). Now,
only the DumpAsText and DumpAsXML formats set it to true. Patch from Patrice
Dumas.
Timestamp v3.27.
Increment to v3.28.
Don't use done_testing.
Fix improper test skip calculation.

When HTML::Entities not installed.
Timestamp v3.28.
Increment to v3.29.
Avoid "unsupported encoding" test failure on Perl 5.6.
No need to require constant, as we do not use it.
typo fix
typo fix
typo fixes
typo fix