Python interpreter and libraries/headers detection.

- The user can now pass its own interpreter.
- Development libraries and headers can be requested.
- Travis-CI switched to new container-based workers.

modules/python_interpreter.cmake

@@ -0,0 +1,36 @@
+#.rst:
+#
+# Detects Python interpreter.
+#
+# Variables used::
+#
+#   PYTHON_INTERPRETER         - User-set path to the Python interpreter
+#
+# Variables defined::
+#
+#   PYTHONINTERP_FOUND         - Was the Python executable found
+#   PYTHON_EXECUTABLE          - path to the Python interpreter
+#   PYTHON_VERSION_STRING      - Python version found e.g. 2.5.2
+#   PYTHON_VERSION_MAJOR       - Python major version found e.g. 2
+#   PYTHON_VERSION_MINOR       - Python minor version found e.g. 5
+#   PYTHON_VERSION_PATCH       - Python patch version found e.g. 2
+#
+# autocmake.cfg configuration::
+#
+#   docopt: --python=<PYTHON_INTERPRETER> The Python interpreter (development version) to use. [default: ''].
+#   define: '-DPYTHON_INTERPRETER="%s"' % arguments['--python']
+
+if("${PYTHON_INTERPRETER}" STREQUAL "")
+    find_package(PythonInterp REQUIRED)
+else()
+    if(NOT EXISTS "${PYTHON_INTERPRETER}")
+        find_program(PYTHON_EXECUTABLE NAMES ${PYTHON_INTERPRETER})
+        if (NOT EXISTS "${PYTHON_EXECUTABLE}")
+            set(PYTHONINTERP_FOUND FALSE)
+        endif()
+    else()
+        set(PYTHONINTERP_FOUND TRUE)
+        set(PYTHON_EXECUTABLE "${PYTHON_INTERPRETER}")
+    endif()
+endif()
+find_package(PythonInterp REQUIRED)