Merge branch 'md_hmac' into development

* md_hmac: (21 commits)
  Add more tests for MD utility functions
  Rework documentation of MD layer
  Check return value of the TLS PRF
  Make tls1_prf and tls12_prf more efficient
  Factor tls_prf_sha{256,384} together
  Reintroduce md_init_ctx compatibility wrapper
  Rename md_init_ctx() to md_setup()
  Update doxygen documentation on HMAC
  Clean up unneeded things
  Make hmac_ctx optional
  Make ipad/opad dynamic and more opaque
  Remove ipad and opad from specific md contexts
  Remove specific xxx_hmac functions
  Remove use of xxx_hmac() in program
  Remove calls to xxx_hmac() from SSL modules
  Remove references to xxx_hmac() from MD layer
  Remove tests for xxx_hmac()
  Implement hmac in the MD layer
  Add generic HMAC tests from mdx.data
  Fix tests and programs to use md_get_xxx()
  ...