Unify zipfile implementations : Step 1.

Extract zip file processing logic from libdvm into a
standalone library.

This library is a stricter than the libdvm library in
several ways:
- Duplicate zip entry names are now disallowed. Files with
  such entries will fail to parse.
- We now verify CD file size information with the individual
  file header information. (This was pointed out as a deficiency
  of this implementation in past discussions.)
- We also add support for crc checking, which means we might
  need to parse the optional data descriptor footer (if one
  exists).

We also provide an API for iterating over the entries of
a zip file. This library is optimized for two use cases :

- Lookup for a single entry in the file, with the intention
  of processing or extracting the data associated with that
  entry
- Iterating over all entries in a file *and* processing
  / extracting their data.

Change-Id: Ia87de6184ef753cc470b0af755c47a4f92ac8198