Refactor dev.sh

- Parameterise the Python version. All of these now work:
    ./dev.sh            # Use default Python version
    ./dev.sh 2.7        # Explicitly use 2.7 in venv2.7
    ./dev.sh 3.5        # Explicitly use 3.5 in venv3.5

This should also work for Travis, which has a weird setup where Pytho3 can be
3.4.

.gitignore

@@ -1,8 +1,7 @@
 .DS_Store
 MANIFEST
 */tmp
-/venv
-/venv3
+/venv*
 *.py[cdo]
 *.swp
 *.swo

dev.sh

@@ -1,29 +1,16 @@
 #!/bin/sh
 set -e
 
-VENV="./venv"
-VENV3="${VENV}3"
+PYVERSION=$1
+VENV="venv$1"
 
-python -m virtualenv $VENV --always-copy
-. $VENV/bin/activate
-pip install -q -U pip setuptools
-pip install -q -r requirements.txt
+echo "Creating dev environment in $VENV using Python $PYVERSION"
+
+python$PYVERSION -m virtualenv "$VENV" --always-copy
+. "$VENV/bin/activate"
+pip$PYVERSION install -q -U pip setuptools
+pip$PYVERSION install -q -r requirements.txt
 
 echo ""
 echo "* Virtualenv created in $VENV and all dependencies installed."
 echo "* You can now activate the $(python --version) virtualenv with this command: \`. $VENV/bin/activate\`"
-
-if $(python --version 2>&1 | grep -q "Python 2.") && command -v python3 >/dev/null 2>&1; then
-	echo ""
-	echo ""
-	
-  python3 -m virtualenv "$VENV3" --always-copy
-	. "$VENV3/bin/activate"
-	pip install -q -U pip setuptools
-	pip install -q -r requirements.txt
-
-	echo ""
-	echo "* Virtualenv created in $VENV3 and all dependencies installed."
-  echo "* You can now activate the $(python --version) virtualenv with this command: \`. $VENV3/bin/activate\`"
-fi
-