[m2sci] kernel misc. fixes & improvements

[m2sci] kernel misc. fixes & improvements

  * %..operatio => %..operation fixed: ttypes are no longer limited to 8 chars

  * sciparam: after https://codereview.scilab.org/21606
              new codes for cells concatenations with braces.

  * Function, Builtin : New predefined constants, required for instance
    to distinguish nargin(@cos) from nargin('cos')
    Not defined anywhere else in [m2sci].

  * Colon : New predefined Variable (to ease definitions of
    insertions and extraction with ":").
    Not defined anywhere else in [m2sci].

  * Help pages: various improvements, noticeably: examples added.

Change-Id: I60e74c2c6980980650023ae8bd6bc49ea4247891