Refactored Caching, Refactored BnfNodeParser, Introduced Sphinx

docs/source/blog/concepts.rst

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+Concepts
+========
+
+
+
+Basic definition
+****************
+To define a new concept
+
+::
+
+    > def concept hello a as "hello" + a
+
+
+Note that if the left part of the keyword 'as', the traditional quotes that would surround 'hello' and 'a' are not necessary.
+In this example 'a' is a variable, as it appears as variable in the 'as' section (while hello
+appears as a string)
+
+You have just defined a concept name 'hello'. Sheerka now can understand
+
+>>> hello kodjo
+>>> hello my friend
+
+When you do so, an instance of the concept will be created in memory. In the first case,
+it will a variable ``'a'`` filled with the value ``'kodjo'``, in the second case, the variable
+will be filled with the value ``'my friend'``
+
+
+Another example:
+
+::
+
+    > def concept one as 1
+    > def concept two as 2
+    > def concept a plus b as a + b
+
+That's enough to define the addition
+
+>>> one plus two
+3
+
+