Move functions to fitfunctions

Refs #9678

Code/Mantid/docs/source/algorithms/Fit-v1.rst

@@ -48,7 +48,7 @@ set before any other.
 
 The function and the initial values for its parameters are set with the
 Function property. A function can be simple or composite. A `simple
-function <../categories/Functions.html>`__ has a name registered with Mantid
+function <../fitfunctions/categories/Functions.html>`__ has a name registered with Mantid
 framework. The Fit algorithm creates an instance of a function by this
 name. A composite function is an arithmetic sum of two or more functions
 (simple or composite). Each function has a number of named parameters,
@@ -74,7 +74,7 @@ To use a simple function for a fit set its name and initial parameter
 values using the Function property. This property is a comma separated
 list of name=value pairs. The name of the first name=value pairs must be
 "name" and it must be set equal to the name of one of a `simple
-function <../categories/Functions.html>`__. This name=value pair is followed
+function <../fitfunctions/categories/Functions.html>`__. This name=value pair is followed
 by name=value pairs specifying values for the parameters of this
 function. If a parameter is not set in Function it will be given its
 default value defined by the function. All names are case sensitive. For
@@ -96,7 +96,7 @@ are created when the Formula attribute is set. It is important that
 Formula is defined before initializing the parameters.
 
 A list of the available simple functions can be found
-`here <../categories/Functions.html>`__.
+`here <../fitfunctions/categories/Functions.html>`__.
 
 Setting a composite function
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