contrib: new filter-repo demo named filter-lamely (or filter-branch-ish)

This is a re-implementation of git-filter-branch that is nearly
perfectly bug compatible (it can replace git-filter-branch and still
pass the git testsuite).  It deviates in one minor way that should not
matter to real world usecases, but allows it to run a few times faster
than filter-branch.

Signed-off-by: Elijah Newren <[email protected]>

Author: newren

contrib/filter-repo-demos/README.md

@@ -13,6 +13,7 @@ insert-beginning     |Add a new file (e.g. LICENSE/COPYING) to the beginning of
 signed-off-by        |Add a Signed-off-by tag to a range of commits
 lint-history         |Run some lint command on all non-binary files in history.
 clean-ignore         |Delete files from history which match current gitignore rules.
+filter-lamely (or filter‑branch‑ish) |A nearly bug compatible re-implementation of filter-branch (the git testsuite passes using it instead of filter-branch), with some performance tricks to make it several times faster (though it's still glacially slow compared to filter-repo).
 
 ## Purpose
 

contrib/filter-repo-demos/filter-branch-ish

@@ -0,0 +1 @@
+filter-lamely