Feature/add options

Note: requires modifying of rspec_command for this to work although should be backwards compatible.

Added the ability to pass different options into the various rspec commands. In order to demonstrate the usefulness of this, consider my test bindings:

```
map <Leader>t :call RunCurrentSpecFile()<CR> " Run all specs in current file
map <Leader>T :call RunCurrentSpecFileWithOptions("--tag=~integration")<CR> " Run all specs in current file apart from ones tagged as integration (for me, slow selenium tests)
map <Leader>s :call RunNearestSpec()<CR> " Run nearest spec
map <Leader>l :call RunLastSpec()<CR> " Run last spec (should work fine with options)
map <Leader>a :call RunAllSpecsWithOptions("--tag=~integration")<CR> " Run all specs apart from integration ones
map <Leader>A :call RunAllSpecs()<CR> " Run all specs
```

Would be interested to see how others use this, I find it really useful.