Simplify conversion of g:tagbar_iconchars into regexp.

With join() and escape(), the steps can be simplified.
FIX: Avoid that the sigils used for highlighting match inside a tag.

When there's a tag e.g. "foo-bar", the "-bar" part is matched as TagbarKind. Add a zero-width condition to all sigil patterns that allow only whitespace characters before the sigil.
FIX: Avoid matching public / private methods as TagbarKind.

When g:tagbar_iconchars = ['+', '-'] (default on Windows), and viewing a filetype (e.g. java) that has visibility information (i.e. the [-+#] sigils), the method is mistakenly highlighted as TagbarKind. Restrict its matches to when the sigil is at the beginning of the line to avoid the false matches at the indented method tags.
Fix TagbarScope pattern
Merge branch 'inkarkat-enh-syntax'