doc: fix typos in ABI policy

doc: fix typos in ABI policy

Some errors in the document:

  * API instead of ABI once.

Some typos:

  * __rte_depreciated instead of __rte_deprecated.
  * missing ```` around value.
  * inconsistent reference to major ABI version, most
    of the time described without the minor appended, except once.

Verbosity and grammar:

  * Long sentences that would be better cut short.
  * Comma abuse.
  * 'May' used where 'can' seems more fitting.

I'm not a native speaker though, so grain of salt applies.

Fixes: fdf7471cccb8 ("doc: introduce major ABI versions")
Cc: stable@dpdk.org
Signed-off-by: Gaetan Rivet <grive@u256.net>
Acked-by: Ray Kinsella <mdr@ashroe.eu>