move bump into the library
refactor bump package function

1) refactor bump into bumpPackage and a zipWith call

2) write tests for bumpPackage

3) add note to test the bumpPackage function when the package version in
the repos is newer than the one on hackage
implement packageVersionString

1) implement with tests

2) replace where necessary
add test for getPackageString
rename getDependencyStringTest0 to getDependencyStringTest_hasDependency and getDependencyStringTest1 to getDependencyStringTest_noDependency
add test for bump
whitespace
add tests for getPkgVertices
simplify buildDependVertices and explicitly call out Data.Maybe functions we should import