Add diff example
Add minimal flag
Add diff format options
added `diff(repo::Repository, left::String, right::GitIndex, opts=nothing)`
simple clone example
Change patch format also in tests
Correct method errors
Merge pull request #6 from elehcim/test_throws

Correct MethodErrors
Merge pull request #5 from elehcim/elehcim/examples

Examples of diff and clone
clean up clone example a bit
clean up oid.jl, mostly formatting changes
use api function for oid comparison
use id as parameter name as oid is a valid function
refactor tree.jl a bit
better walk order error message
refactor a bit more, adopting short circuting control flow convention
tweak runtests.jl
rename pointers to prevent name clash with arg
refactor blob, rawcontent now returns an array of bytes
tweak diff example