Format data based on type

Using postgis, geom data is not correctly showed, and you cannot export it to sql

using a format like 

    st_AsText($colname)

can create a text value ready to read

for insert you need something like

    'ST_GeomFromText(' || st_AsText($colname)|| ' , ' || st_srid($colname) || ' )'

There can be more placeholders like $value, $type, etc...
