crashsdk v2.1

updates: Add a seprated library towards devices API level above 21 to unwind call stack. Reason below:

For some devices of ARM arch, in which the system native libraries not contain exidx section to unwind call stack. In order to use eh_frame when exidx section not exist , we need 'dl_iterate_phdr' to find out the eh_frame section, this is a system api on ARM and only exist after api level 21. 

crashsdk v2.0

1. Add support for lower android api(lower to 14);
2. Add proguard option to reduce library size;
3. Unwind calling stack by Exidx only, since EhFrame require high level system api to find out .eh_frame section;
4. Add a panel to show crash info;

crash sdk v1.0

first release