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;
5. Add a license;:

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;
5. Add a license;:

Update README.md