Re: add function argument name to substring and substr

hi.

new patch attached.
now \df substring looks like:
                                          List of functions
   Schema   |   Name    | Result data type |               Argument
data types                | Type
------------+-----------+------------------+--------------------------------------------------+------
 pg_catalog | substring | bit              | bits bit, start integer
                       | func
 pg_catalog | substring | bit              | bits bit, start integer,
count integer           | func
 pg_catalog | substring | bytea            | bytes bytea, start
integer                       | func
 pg_catalog | substring | bytea            | bytes bytea, start
integer, count integer        | func
 pg_catalog | substring | text             | string text, pattern text
                       | func
 pg_catalog | substring | text             | string text, pattern
text, escape_character text | func
 pg_catalog | substring | text             | string text, start
integer                       | func
 pg_catalog | substring | text             | string text, start
integer, count integer        | func


Table 9.10 also have doc entry for substring.
in  Table 9.10, i have:
substring ( string text, pattern text ) → text
substring ( string text, pattern text, escape_character text) → text

we can put it into one,
but one is based on POSIX regular expression, another one is based on SQL,
the difference is big, that's why put it into two.