adding doc/library/compile io and mode

doc/library/compile/mode.txt

+======================================
+:mod:`mode` -- controlling compilation
+======================================
+
+.. module:: mode
+   :platform: Unix, Windows
+   :synopsis: controlling compilation
+.. moduleauthor:: LISA
+
+Guide
+=====
+
+The ``mode`` parameter to :func:`theano.function`` controls how the
+inputs-to-outputs graph is transformed into a callable object.
+
+Theano defines the following modes by name:
+
+- ``FAST_COMPILE``: Apply just a few optimizations, but use C op implementations where possible.
+- ``FAST_RUN``: Apply all optimizations, and use C op implementations where possible.
+- ``DEBUG_MODE``: Verify the correctness of all optimizations, and compare C and python 
+    implementations. This mode can take much longer than the other modes, 
+    but can identify many kinds of problems.
+
+The default mode is typically 'FAST_RUN', but it can be controlled via the
+environment variable 'THEANO_DEFAULT_MODE', which can in turn be overridden by
+setting ``theano.compile.mode.default_mode`` directly, which can in turn be
+overridden by passing the keyword argument to ``theano.function``.
+
+For a finer level of control over which optimizations are applied, and whether
+C or python implementations are used, read :api:`compile.mode.Mode`.
+
+
+Reference
+=========
+
+.. attribute:: FAST_COMPILE
+
+.. attribute:: FAST_RUN
+
+.. attribute:: DEBUG_MODE
+
+.. attribute:: PROFILE_MODE
+
+.. class:: Mode(object)
+
+    Compilation is controlled by two attributes: the `optimizer` controls how
+    an expression graph will be transformed; the `linker` controls how the
+    optimized expression graph will be evaluated.
+
+    .. attribute:: optimizer
+
+        An :class:`optimizer` instance.
+
+    .. attribute:: linker
+
+        A :class:`linker` instance.
+
+    .. method:: including(*tags)
+
+        Return a new Mode instance like this one, but with an
+        optimizer modified by including the given tags.
+
+    .. method:: excluding(*tags)
+
+        Return a new Mode instance like this one, but with an
+        optimizer modified by excluding the given tags.
+
+    .. method:: requiring(*tags)
+
+        Return a new Mode instance like this one, but with an
+        optimizer modified by requiring the given tags.
+