v23.01 release

* Project changes
  * All files are under a new dual license now (MIT OR Apache-2.0 WITH
    LLVM-exception at the election of the user).
  * Added MAINTAINERS file describing who maintains the subdirectories.
  * Added README.contributors files documenting contribution
    requirements.
  * Added new pl/ subdirectory for Arm's Performance Library related
    routines.
* String routine changes
  * Added memset benchmark.
  * Improved strlen and memcpy benchmarks.
  * Added SVE memcpy.
  * Updated arm string functions to support M-profile PACBTI.
  * Merged the MTE and generic versions of strcmp, strncmp, strcpy and
    stpcpy into one implementation.
  * Optimized memcmp, memchr-mte, memrchr, strchr-mte, strchrnul-mte,
    strrchr-mte, strlen, strlen-mte, strnlen, strcpy.
* Math routine changes
  * Fixed constants in sinf, cosf and sincosf to be compile time
    computed even with gcc-12 -frounding-math.
  * Fixed an invalid shift in logf.
  * Support floating-point exceptions in vector math routines when
    WANT_SIMD_EXCEPT is set.