read:
1. read the ini file in a text object
2. normalize the text object
3. search for your [topic]
4. search for your key=
5. return the value

add/delete:
1. read the ini file in a text object
2. create a temp dest. textobject
3. copy untouched entries to the dest textobject
4. when found your [topic] your key=
change the value(change) or skip copying the line(del)
6. write the dest. textobject