Rename relative_margin to relativeMargin for consistency

[nicoddemus]

Follow up to 0e44c89, I noticed the new parameter name relative_margin does not follow the naming scheme used by the other parameters in the library, so renamed it to relativeMargin.

Relative to #94.

[nicoddemus]

Btw I realize PythonQwt already has a testing setup/framework in-place, just wanted to mention that there's pytest-qt (I'm one of the maintainers) which provides facilities to test Qt code. 👍

[PierreRaybaut]

You're perfectly right.

[PierreRaybaut]

Btw I realize PythonQwt already has a testing setup/framework in-place, just wanted to mention that there's pytest-qt (I'm one of the maintainers) which provides facilities to test Qt code. 👍

Thanks for pointing that out.
Actually, we did test it a while ago but we choose to not depend on it, first to limit the dependencies to the strict minimum, second because we had issues or we encountered some limitations (not on PythonQwt but on PlotPy) but I don't remember what exactly (not very constructive, I'm sorry).