* add new option enable for include of spec
* fix to see the environment variable when parsing include
* add test for include with environment variable
* fix how to parse boolean value
* add spec about enable for include
* add Change Log
* fix the number of PR in changelog
* fix include test to make more clear
* fix test to focus enable option more
* fix english error
* fix to expand variable only one time
* add new test case by setting environment object as NO
* Improving variable expansion runtime
The current implementation of variable expansion is O(n x m) with n being the
number of strings in the project spec and m being the number of project variables.
This implementation is now O(n).
Also, this effectively deprecates the support for $legacy_variables in favor of the
${new_variables} making this whole patch possible.
* Adding option to disable variable expansion
* Adding performance test for spec loading
* Updating changelog
freddi(Yuki Aki)
Akio Yasui
yonaskolb
Romuald Cari
Brian Clymer
Brian Clymer
Yuta Saito
haritowa
Tom Quist