Working on improving sith.py run

As discussed at https://github.com/davidhalter/jedi/issues/274. So far, I have
modified sith.py run to print the location and completions. For example

```
$./sith.py run completions sith.py 72 13
70         self.line = line
71         self.column = column
72         self.traceback = traceback
                ^
Completions:
column
completions
file
from_cache
generate
line
mro
operation
path
run
script
show_completions
show_errors
show_location
traceback
__class__
__delattr__
__format__
__getattribute__
__hash__
__init__
__new__
__reduce__
__reduce_ex__
__repr__
__setattr__
__sizeof__
__str__
__subclasshook__
```

Don't merge this yet. I haven't completely tested it, and I plan to add more
stuff.