Improve the documentation for chebfun.norm().
Improve the documentation for chebfun.norm().

 - Capitalized variable names.
 - Added entries for the -inf and p-norms of array-valued chebfuns.
 - Improved the explanation of the second output for the relevant norms of
   array-valued chebfuns.
 - Added a remark regarding how row chebfuns are handled.  This is especially
   important for understanding how operation for array-valued chebfuns is
   supposed to work.

ilovejs/chebfun,asgeirbirkis/chebfun,alshedivat/chebfun