Add manual and docstring-parsed tooltips

[tlambert03]

This closes #94 by adding an option to provide a tooltip parameter to any widget. When using with a magicgui decorator, tooltips will be parsed (by default) from the first sentence of the corresponding parameter description in the docstring (ReST, google and numpy docstrings supported). Auto-tooltips can be turned off using magicgui(tooltips=False), or overridden for each parameter specifically.

# during widget creation:
widget = LineEdit(tooltip="Enter a value")

# with magicgui
@magicgui(x={"tooltip": "override tooltip"}, z={"tooltip": None})
def func(x: int, y: str = "hi", z=None):
    """Do a little thing.

    Parameters
    ----------
    x : int
        An integer for you to use
    y : str, optional
        A greeting, by default 'hi'. Only the first sentence
        will be used. Even if the docstring is very long, etc...
    z : Any, optional
        No tooltip for me please.
    """
    pass

assert func.x.tooltip == "override tooltip"
assert func.y.tooltip == "A greeting"  # the "by default" part is also stripped
assert not func.z.tooltip

[tlambert03]

most of this is just moved in this PR... only new things is the tooltip property

[codecov]

Codecov Report

Merging #100 (8c9030c) into master (50f6829) will decrease coverage by 0.13%.
The diff coverage is 89.28%.

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
- Coverage   86.16%   86.03%   -0.14%     
==========================================
  Files          15       14       -1     
  Lines        1728     1740      +12     
==========================================
+ Hits         1489     1497       +8     
- Misses        239      243       +4     

Impacted Files	Coverage Δ
magicgui/widgets/_protocols.py	75.14% <66.66%> (-0.30%)	⬇️
magicgui/widgets/_bases.py	88.43% <84.37%> (+0.15%)	⬆️
magicgui/function_gui.py	94.81% <94.44%> (-0.06%)	⬇️
magicgui/widgets/_concrete.py	81.70% <95.65%> (+0.88%)	⬆️
magicgui/backends/_qtpy/widgets.py	81.88% <100.00%> (+0.26%)	⬆️
magicgui/types.py	100.00% <100.00%> (ø)
magicgui/signature.py	95.18% <0.00%> (-2.41%)	⬇️
magicgui/type_map.py	89.40% <0.00%> (+0.66%)	⬆️

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[tlambert03]

@haesleinhuepf, you had expressed an interest in this. have a look at the API above and let me know if you have any thoughts

[jni]

❤️