Improve the migration script and guide (#166)

- Safer replacement of 'graph' and 'edge'.
- Fix the erroneous renaming of [Gg]raphToEps.
- Fixes and improvements in the migration guide.

 if WANT_TOOLS

 bin_PROGRAMS +=

 dist_bin_SCRIPTS += tools/lemon-0.x-to-1.x.sh

 endif WANT_TOOLS