Check for commonly misspelled words during the CI build

Use codespell to check for commonly misspelled words during the Travis CI build. In the event of false positives, the words can be added to extras/codespell-ignore-words-list.txt, after which codespell will ignore those words.

Author: per1234

.travis.yml

@@ -48,6 +48,18 @@ matrix:
         # check code formatting
         - find . -regextype posix-extended -path './.git' -prune -or \( -iregex '.*\.((ino)|(h)|(hpp)|(hh)|(hxx)|(h\+\+)|(cpp)|(cc)|(cxx)|(c\+\+)|(cp)|(c)|(ipp)|(ii)|(ixx)|(inl)|(tpp)|(txx)|(tpl))$' -and -type f \) -print0 | xargs -0 -L1 bash -c 'if ! diff "$0" <(astyle --options=${HOME}/astyle/examples_formatter.conf --dry-run < "$0"); then echo "Non-compliant code formatting in $0"; false; fi'
 
+    # check all files for commonly misspelled words
+    - env:
+        - NAME='Spell Check'
+      language: python
+      python: 3.6
+      before_install:
+        # https://github.com/codespell-project/codespell
+        - pip install codespell
+      script:
+        # codespell will ignore any words in extras/codespell-ignore-words-list.txt, which may be used to fix false positives
+        - codespell --skip="${TRAVIS_BUILD_DIR}/.git" --ignore-words="${TRAVIS_BUILD_DIR}/extras/codespell-ignore-words-list.txt" "${TRAVIS_BUILD_DIR}"
+
 # default phases shared by the compilation tests
 before_install:
   - wget http://downloads.arduino.cc/arduino-cli/arduino-cli-$CLI_VERSION-linux64.tar.bz2