Added generic function SYMBOL-MACRO-EXPANSION and methods on it.
Export name SYMBOL-MACRO-EXPANSION.
Added method on CLEAVIR-ENV:SYMBOL-MACRO-EXPANSION.
New component containing other environment functions.
Added definition of SICL-ENV:GET-SETF-EXPANSION.
Shadow and export name GET-SETF-EXPANSION.
Return original form if no symbol macro exists.
Use new function SICL-ENV:GET-SETF-EXPANSION.