[Fix #1289] Use utf-8 as default encoding for inspected files

For all Ruby versions.
Merge pull request #1322 from jonas054/1289_default_encoding

[Fix #1289] Use utf-8 as default encoding for inspected files
[Fix #1304] Style/Encoding is no longer a no-op on Ruby 2.x

It's also disabled by default, as projects not supporting 1.9 don't need
to run it.
Make it possible to ignore certain methods in SymbolProc
Cut 0.26.0