Fixed the podspec in order to stop disabling exceptions project-wide (#78).

Moved the offending build settings from "xcconfig" to equivalents in "compiler_flags" so that they affect the zipzap source files only, and don't contaminate the rest of the host project.
Adjusted podspec to split the source into two subspecs, for each of objc and objc++ respectively, in order to allow distinct compiler flags to be specified for each group. (#78/#83)
Merge pull request #83 from zygoat/tolerate_exceptions

Fixed the podspec in order to stop disabling exceptions project-wide (#78).