require-space-after-line-comment: add except option

according to #592 and #593 we've decided to make allExcept option to this rule to pass there a list of allowed characters

- added allExcept option to pass here exceptions
- fixes initial #592 bug with tabs in line comments
- add validation of allExcept (should be a <String[]>, according to #698)

Closes #696
Fixes #592
require-space-after-line-comment: tests and update readme for except

- add docs about allExcept
- deprecate allowSlash (and issue #696 to drop it)
- tests for #592