PR: Aliased QUndoCommand, provided QLineEdit.getTextMargins() and QFontMetricsF.width()

[random-developer]

Fixes #365

[dalthviz]

Thanks @random-developer for your help with this! I think the only missing thing here is to add some testing:

• For QtWidgets.QUndoCommand and QtWidgets.QLineEdit.getTextMargins at: https://github.com/spyder-ide/qtpy/blob/master/qtpy/tests/test_qtwidgets.py
• For QtGui.QFontMetricsF.width at: https://github.com/spyder-ide/qtpy/blob/master/qtpy/tests/test_qtgui.py similar to

  qtpy/qtpy/tests/test_qtgui.py

  Lines 14 to 20 in fdd6818

  	def test_qfontmetrics_width(qtbot):
  	"""Test QFontMetrics width"""
  	assert QtGui.QFontMetrics.width is not None
  	font = QtGui.QFont("times", 24)
  	font_metrics = QtGui.QFontMetrics(font)
  	width = font_metrics.width("Test")
  	assert width in range(40, 62)

Other than that this looks good to me 👍

[random-developer]

The QUndoCommand test is failing. I'm not sure why; will investigate later; too pressed for time right now.

[dalthviz]

Thanks @random-developer ! This LGTM 👍