Restore support for older Ruby

Latest merge broke support for Ruby 1.8.7, which is still required
by some gems that depend or use mini_portile.

Attempt to restore its functionality with minor modifications.
Use SSL_CERT_FILE for HTTPs connection if present

Ruby's OpenSSL in version 1.8.7 had a problem that wouldn't pick
automatically SSL_CERT_FILE and required manual setting as `ca_file`
on the HTTP instance.

This attempts to workaround this issue for those poor souls that
are still using Ruby 1.8.7 and need to download stuff from HTTPS
connections.
Refactor recipe example to reduce duplication

Dynamically adjust list of recipes
Add another recipe example (c-ares)

- Download from Knapsack S3 repository
- Use HTTPS (so SSL can be tested)
Perform tests by compiling example ports

Creating tests for autoconf/autotools based libraries is hard.

Since we need to ensure this code keeps working across different
versions of Ruby, let's run some sort of *integration tests*
against the example recipes.
Update history and bump version

Preparation for another release.

v0.5.4 was skipped due incorrect tagging and testing.
Add Travis configuration file