doc: update conversions

- conversions were documented in the manpage
- added the same doc to README
- fixed the lookup of manpage to search in the same folder as the script

fix integer command

'int' command would get the int part of a flot, but it was storing it
back in the stack as int, thus messing with the conversions done
internally. Adding an str() fixes it.

update readme with macro example

Signed-off-by: bleader <[email protected]>

v0.3 - first release

make it work from stdin

Signed-off-by: bleader <[email protected]>

First really useable version.