v7: PowerPC support

Support for PowerPC (ppc32 & ppc64), along with hwcap dumping tool and tests.

v6

• x86: add tests
• x86: add 'sha' flag

v5

• arm: support non-glibc systems with getauxval()
• x86: support non-GNUC compilers with cpuid.h
• x86: add pclmul flag (thanks to Vivek Jindal)

v4

Minor improvements, documentation:

• added a README file with usage instructions and technical details,
• short-circuited 32-bit code on pure AArch64 target,
• added explicit error on unknown ARM architecture and uname() failure.

v3

ARM (& aarch64) support!

v2

Rewritten in C using CPUID intrinsic.

v1

Initial Python version