f2fscrypt: add a tool for encryption management in the f2fs filesystem

It's migrated from e4crypt.
Adds an example to the f2fscrypt manpages.

v3, add /tools/f2fscrypt to .gitignore
v2, migrate those micro defines for encrypt to f2fs internal,
    drop unless of libsha etc.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/.gitignore b/.gitignore
index debeffb..abe1336 100644
--- a/.gitignore
+++ b/.gitignore
@@ -49,3 +49,4 @@
 /tools/f2fstat
 /tools/fibmap.f2fs
 /tools/parse.f2fs
+/tools/f2fscrypt