Add test target to Makefile

easy way to run the tests without installing the library
Fix lfs.attributes(file, 'blksize')

fs.attributes(file, 'blksize') and fs.attributes(file, 'blocks) return
the wrong values.
Compare the whole attribute name instead of the first char and remove
buggy special casing with wrong indexes into the member array.
Merge pull request #44 from stefan991/fix-attribute-lookup

Fix attributes `blksize` and `blocks`