Read timezone data from text files and serialize with Pkg.build

This pull request removes the binary files in `src/tzdata` and replaces them with text versions.  The binary files are recreated on install by `deps/build.jl`, which reads the text files and serializes them. `src/Datetime.jl` and `src/Timezone.jl` can then access the data in `src/tzdata` without change, fixing #50.

The tests pass before and after JuliaLang/julia@bb67ff2.  I also confirmed on a julia version prior to JuliaLang/julia@bb67ff2 , the binary files generated by Pkg.build are identical to those removed from `src/tzdata`.

The build program could be cleaned up a bit I'm sure, but it does the job.