Features
   * Added partial support for parsing the PKCS7 cryptographic message syntax,
     as defined in RFC 2315. Currently, support is limited to the following:
     - Only the signed data content type, version 1 is supported.
     - Only DER encoding is supported.
     - Only a single digest algorithm per message is supported.
     - Only 0 or 1, certificate is supported per message, which must be in
       X509 format.
     - There is no support for certificate-revocation lists.
     - The authenticated and unauthenticated attribute fields of SignerInfo
       must be empty.
     Many thanks to Daniel Axtens, Nayna Jain, and Nick Child from IBM for
     contributing this feature.

Add changelog for PKCS7 parser
Add changelog for PKCS7 parser

Signed-off-by: Bence Szépkúti <f5a052dc170d15117fd347c2abf2400eb6ae5243@arm.com>
