Introduce AE_FEATURE to manage configure features

The new AE_FEATURE set of macros are wrappers over autoconf's
AC_ARG_ENABLE. The main objective is to make the m4sh code more readable
to the less seasoned autotools enthusiast among us and reduce the
duplication of code with its associated bugs.

The AE prefix was chosen to mean "Autotools EfficiOS" and is part of an
effort to standardize our custom macros across all our autotools based
projects.

Change-Id: Ief565473b38150fe2104492c6339bac73efba895
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>