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
Add feature: switch back to clojure buffer

Try to remember the clojure buffer before
nrepl/nrepl-jack-in/nrepl-swith-to-nrepl-buffer,
so that the user could jump back to the original
clojure buffer from the repl buffer. The key binding
is also C-c C-z, which makes it convenient to
jump between clojure and repl buffers.
Merge pull request #344 from moonranger/switch-to-clojure-buf-squashed

Add feature: switch back to clojure buffer
Update copyright and extend contributing section a bit
Move from cl to cl-lib

Since Emacs 24.3 the use of cl is discouraged and cl-lib is now
considered the way to go.

This fixes #319 and all outstanding compilation warnings.
Replace first, second and rest with car, cadr and cdr

This is part of the migration to cl-lib.
Always evaluate ns forms in the user namespace.

This allows ns forms to be interactively evaluated to create new
namespaces without them having had to already exist through other
means. This is something I almost always find myself doing in a live
coding workflow.