Instead of a script which generates macros, emit static inlines in
individual header (or C files). This solves a few issues with the
original setup:

- The documentation was off. We match the documentation now.

- The stack macros did not check constness; see some of the fixes in
  crypto/x509.

- Type errors did not look like usual type errors.

- Any type which participated in STACK_OF had to be made partially
  public. This allows stack types to be defined an internal header or
  even an individual file.

- One could not pass sk_FOO_free into something which expects a function
  pointer.

Thanks to upstream's 411abf2dd3 for the
idea.

Change-Id: Ie5431390ccad761c17596b0e93941b0d7a68f904
Reviewed-on: https://boringssl-review.googlesource.com/16087
Reviewed-by: Adam Langley <agl@google.com>