Use (nrepl-current-ns) rather than nrepl-buffer-ns for interactive eval

When visiting a file for the first time, nrepl-buffer-ns is set to
"user" which made interactive eval commands such as
nrepl-eval-last-expression slightly surprising as they wouldn't be
evaluated in the current buffer's namespace. This patch now
uses (nrepl-current-ns) instead which should do the right thing.
Enhanced error highlighting, errors in red, warnings in yellow.
fix handling of missing column better
Hook into `paredit-space-for-delimiter-predicates`

This prevents paredit from inserting spaces after '#' in '#(', '#{',
'#"'.

C.f. https://github.com/technomancy/clojure-mode/commit/8699952eb18ab4c739e8f7462b3326d93bd0095c
Don't try to switch namespace if we don't know which one to switch to.

- `clojure-find-ns` is sometimes unable to figure out what the current
  namespace is. If that's the case, don't try to switch (avoids nasty
  exception) and show a friendly message
Merge pull request #307 from sw1nn/enhanced-error-highlighting

Enhanced error highlighting, errors in red, warnings in yellow.
Merge pull request #333 from happy4crazy/paredit-bug

Hook into `paredit-space-for-delimiter-predicates`
Merge pull request #340 from ragnard/fix-nrepl-set-ns-with-unknown-ns

Don't try to switch namespace if we don't know which one to switch to.
Update TravisCI URL
Update project URL
Remove a few tabs
Take care of a compilation warning
Take care of a compilation warning
Merge pull request #309 from DerGuteMoritz/use-current-ns-for-interactive-eval

Use (nrepl-current-ns) rather than nrepl-buffer-ns for interactive eval