Allow running a block of code in a file

[ghost]

It would be great if there is a way to run only a "block" of code in a file.

For example,

%run 'file.py' 100:200 # run code in file.py from line 100 to 200

or

%run 'file.py' :200 # run code in file.py from line 1 to 200

etc.

Thank you,
Joon

[minrk]

This is a close relative of the request described in #403. If either is implemented, they both will be, so please make any further comments/requests there.