added documentation regarding theano's core

doc/core_development_guide.txt

+
+Core Development Guide
+=======================
+
+The documentation of the core components of Theano is still a work in
+progress. For now this is a list of bits and pieces on the subject, 
+some of them might be outdated though:
+
+
+* :ref:`theano_type` -- tutorial for writing a new type in Theano. It introduces the
+basics concerning Theano datatypes
+
+* :ref:`theano_ctype` -- tutorial on how to make your type C friendly. 
+
+* :ref:`views_and_inplace` -- this is somewhere between extending theano and
+describing how theano works internally; it talks about views and inplace
+operations
+
+* :ref:`optimization` -- tutorial on how optimization work in Theano 
+
+* :ref:`pipeline` -- describes the steps of compiling a Theano Function
+
+* :ref:`graphstructure` -- describes the symbolic graphs generated by scan
+
+* :ref:`unittest` -- tutorial on how to use unittest in testing Theano
+
+* :ref:`sandbox_broadcasting` -- short description of what a broadcastable
+ pattern is
+
+* :ref:`sandbox_debugging_step_mode` -- how to step through the execution of
+ a thenao function and print the inputs and outputs of each op
+
+* :ref:`sandbox_elemwise` -- description of element wise operations
+
+* :ref:`sandbox_maxgotcha` -- describes the difference between numpy.max and
+ python max (something to consider when using max)
+
+* :ref:`sandbox_randnb` -- description of how Theano deals with random
+ numbers
+
+* :ref:`sparse` -- description of how the sparse type in Theano
+

doc/extending/ctype.txt

+.. _theano_ctype:
+
 
 ========================
 Implementing double in C

doc/extending/type.txt

-
+.. _theano_type:
 
 ======================
 Making the double type

doc/sandbox/broadcasting.txt

+.. _sandbox_broadcasting:
 
 The following may go either in:
 a) numpy refresher.

doc/sandbox/debugging_with_stepmode.txt

 
+.. _sandbox_debugging_step_mode:
+
 Debugging with a customized so-called StepMode
 ==============================================
 

doc/sandbox/elemwise_compiler.txt

+.. _sandbox_elemwise:
+
 '''Stale specification page.  Upgrade this to provide useful developer doc. 2008.09.04'''
 == Definitions ==
 

doc/sandbox/max_gotcha.txt

+.. _sandbox_maxgotcha:
+
 Guillaume and I just found a bug in some experiment code that was
 basically caused by confusing semantics of max().  The same sort of
 thing applies to min.  This is an FYI email to help others on the list

doc/sandbox/randomnumbers.txt

+.. sandbox_randnb:
 
 ''' This has been implemented (#182). 20090327.'''