Add travis-ci indicator.
Change default value for certificate location.

s/San Diego/Home
Add mandatory extensions to certs

The following two certs make debugging problems a lot easier and are now
mandatory for all certs generated with this library.

  - subjectKeyIdentifier
  - authorityKeyIdentifier

More information available at
https://www.openssl.org/docs/apps/x509v3_config.html#Subject_Key_Identifier_