fix missing export lookup_blob
refactor LibGitError, include class and code in type definition for error
fix deprecation warnings for @test_throws in blob.jl tests
make Oid immutable, hex is defined in Base so we remove it from exports list.  Sha type should be a bytestring
refactor tree.jl
refactor tree.jl a bit more
refactor remote.jl a bit
remove git_otype from tag.jl as it was moved to types.jl
refactor walker, GitError has been renamed to LibGitError
fix missing comma, escape orginial function body in @check macro
use GIT_OK constant to make loop exit condition clearer
GitError has been renamed to LibGitError
replace our custom init() function with proper module __init__
fix deprecation warning for @test_throws