Bug fixes

- render module no longer has memory access violation when uninitialized
  before all tracern-like modules have been
- functions now correct their own stack alignment on x86 when SIMD
  instructions are enabled (necessary when using CPython compiled by MSVC)
- under Python 2, get_buffer is now used even if get_view is available because
  get_view does not always yield a writable buffer
- fixed typo in version testing in py_common.cpp that caused link failure
- removed "including AVX 512" from documentation since although the code
  should support it, the relevent macros are not tested to enable it
  automatically