[Fix #997] Make sure paths are on normal form for exclude

Calling "rubocop ." would result in absolute paths with "/./" in them
and matching against Exclude properties failed.
Merge pull request #998 from jonas054/fix_997_dot_argument

[Fix #997] Make sure paths are on normal form for exclude
[Refactor] Extract module OptionsHelp from Options

Put all help texts in one place.
[Refactor] Move methods from ConfigLoader to Config

Takes care of the code smell "Feature Envy" in ConfigLoader and
makes it smaller. Two birds with one stone.
Merge pull request #999 from jonas054/refactor_class_lengths

Refactor for smaller classes
Improve AmbiguousOperator's message
Improve AmbiguousRegexpLiteral's message
Improve BlockAlignment's message
Improve EndAlignment's message
Improve ParenthesesAsGroupedExpression's message
Improve ShadowingOuterLocalVariable's message
Improve UselessAssignment's message
Improve UselessElseWithoutRescue's message
Improve UselessElseWithoutRescue's message