Provide functions to narrow around current-line

It's nice to be able to run Iedit on only the current line or lines
near the current line. Provide functions to narrow the Iedit search
region to the current line and to expand the search region near the
current line ad-hoc.
Merge pull request #38 from mgalgs/narrow-around-current-line

Provide functions to narrow around current-line
A good start point to a more mature functionality