[Suggestion] fs API changes

[EzraJ]

You should make it so we can read a specific line of a file: fs.readLine(1) lets us read the contents of the first line of a file. You should also add an ability to write to a specific line of a file; fs.writeLine(2, "I wrote this to line 2")

[SquidDev]

Might be worth having a look at #504 (namely the seek functionality), which would enable similar functionality.