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.
Add save-window-excursion
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
Option to clean up the occurrence string presented to the user

If `iedit-only-complete-symbol-*' is being used then there are some
extra characters added to the occurrence string which make the string
a regexp to only match symbols. The user might not want to see the
extra characters needed to form the regexp. Provide an option to strip
off the added characters when presenting the occurrence string to the
user.