Refactor build evironments to be compatible with multiple Python versions

tox.ini

@@ -2,17 +2,10 @@
 # See LICENSE for details.
 
 [tox]
-# toxworkdir = /tmp/.tox
-# toxworkdir = C:\Users\User\Downloads\.tox
-envlist = docs, lint, pytest
-
-[testenv]
-envlogdir = /tmp/toxlogdir
-envtmpdir = /tmp/toxtmpdir
-commands =
-    {envpython} --version
+envlist = py26, py27, docs, lint
 
 [testenv:develop]
+basepython = python2.7
 usedevelop = True
 deps =
     isort
@@ -21,15 +14,17 @@ commands =
     pip install --egg http://sourceforge.net/projects/scons/files/latest/download
 
 [testenv:docs]
+basepython = python2.7
 deps =
     sphinx
     sphinx_rtd_theme
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees docs docs/_build/html
     sphinx-build -W -b latex -d {envtmpdir}/doctrees docs docs/_build/latex
-    /bin/bash -c "if [[ $CI != \\"true\\" ]]; then sphinx-build -W -b linkcheck docs docs/_build/html; fi"
+    /bin/bash -c "if [[ '$CI' != 'true' ]]; then sphinx-build -W -b linkcheck docs docs/_build/html; fi"
 
 [testenv:lint]
+basepython = python2.7
 deps =
     flake8
     pylint
@@ -37,11 +32,13 @@ commands =
     flake8 ./platformio
     pylint --rcfile=./.pylintrc ./platformio
 
-[testenv:pytest]
-changedir = tests
+[testenv]
+basepython =
+    py26: python2.6
+    py27: python2.7
 usedevelop = True
-deps =
-    pytest
+deps = pytest
 commands =
+    {envpython} --version
     pip install --egg http://sourceforge.net/projects/scons/files/latest/download
-    py.test -v -s --basetemp={envtmpdir}
+    py.test -v -s --basetemp="{envtmpdir}" tests