BLD: Add platform-specific skips

Add the ability to manually skip appveyor or travis using the commit message

The syntax is:

[skip appveyor]
[skip travis]

.travis.yml

@@ -106,6 +106,10 @@ notifications:
  on_success: always
 
 before_install:
+ # Skip if commit message contains [skip travis] or [travis skip]
+ - COMMIT_MESSAGE=$(git show -s $TRAVIS_COMMIT_RANGE | awk 'BEGIN{count=0}{if ($1=="Author:") count++; if (count==1) print $0}')
+ - if [[ $TRAVIS_PULL_REQUEST == false ]]; then COMMIT_MESSAGE=${TRAVIS_COMMIT_MESSAGE}; fi
+ - if echo "$COMMIT_MESSAGE" | grep -E '\[(skip travis|travis skip)\]'; then exit 0 ; fi
  # Show information about CPU running job to understand BLAS issues
  - sudo lshw -class processor
  # Fix for headless TravisCI

appveyor.yml

@@ -30,6 +30,10 @@ platform:
  - x64
 
 build_script:
+ # Search for [appveyor skip] or [skip appveyor] and exit if found in full commit message
+ - ps: $commit=$env:APPVEYOR_REPO_COMMIT_MESSAGE + $env:APPVEYOR_REPO_COMMIT_MESSAGE_EXTENDED
+ - ps: $skip_appveyor=$commit.Contains("[skip appveyor]") -Or $commit.Contains("[appveyor skip]")
+ - ps: If ($skip_appveyor) { echo "[skip appveyor]"; Exit-AppVeyorBuild }
  # Show information about CPU running job to understand BLAS issues
  - wmic cpu get caption, name, numberofcores
  - SET MKL_NUM_THREADS=1