enable pip cache & non-optimizing cmake for travis (#92)

pip cache & non-optimizing compiling for travis speedups

.travis.yml

@@ -1,12 +1,22 @@
+sudo: false # force container-based builds (no start-up time!)
+
 language: python
+
+cache: pip # enable cache for "$HOME/.pip-cache" directory
+
 before_install:
+  - export CFLAGS=-O0 # considerably speed-up build time for pip packages (especially lxml), optimizations doesn't matter for ci
   - pip install commentjson
   - python verify_files.py # make sure input files are OK before wasting time with prereqs
+
 install:
-  - pip install -r requirements.txt
+  - pip install -r requirements.txt --cache-dir $HOME/.pip-cache
+
 script: bash ./deploy.sh
-after_script:   
+
+after_script:
   - sleep 10 # helps travis finish logging
+
 notifications:
   email: false
   webhooks:
@@ -14,7 +24,8 @@ notifications:
       - https://webhooks.gitter.im/e/691b9acffe1def5f9d6b
     on_success: always  # options: [always|never|change] default: always
     on_failure: always  # options: [always|never|change] default: always
-    on_start: always     # options: [always|never|change] default: always
+    on_start: always    # options: [always|never|change] default: always
+
 deploy:
   provider: releases
   api_key:
@@ -26,6 +37,7 @@ deploy:
   on:
     tags: true
     branch: master
+
 env:
   global:
   - ENCRYPTION_LABEL: ec68c19ba263