Display warnings only when there are no errors messages.

In large code base, typically there will lot of warnings because the
file has been changed by many people and not everyone bothered to follow
coding conventions. So its more useful to show the errors first. Once
all errors have been fixed, we can focus on warnings.
themes: fix GUI murmur theme.
Make tabline's left separators customizable as right separathers.
Merge pull request #619 from bchretien/master

themes: fix GUI murmur theme.
Merge pull request #622 from spacelis/master

Make tabline's left separators customizable as right separathers.
add small section about performance to readme
Merge pull request #618 from rkannan82/master

Display warnings only when there are no errors messages.
Exclude INFO from error/warning count.

Eclim uses signs for code reference searches and they shows up as INFO
signs. These are not errors/warnings and hence should not be included in
count.

Testing:
Verified the right count shows up.