Colors given as tuple of ints are not working anymore for LinearColormap and StepColormap since v0.8.0

从 branca.colormap._parse_color 开始，跟踪 LinearColormap 和 StepColormap 如何将它们的颜色传递给它。复现 issue 中的整数元组示例，然后验证元组是否被规范化为 float 颜色值，以及 rgb_bytes_tuple 和 rgba_floats_tuple 是否为两种 colormap 类型生成预期结果。

When I create a LinearColormap or a StepColormap with a list of tuples of ints as argument for the colors parameter, it is no longer converted to floats and leads to incorrect results.

Current behaviour (v0.8.0 v0.8.1):

>>> from branca.colormap import LinearColormap
>>> colormap = LinearColormap(colors=[(128, 64, 255), (255, 128, 0)])
>>> colormap.colors
[(128, 64, 255, 1.0), (255, 128, 0, 1.0)]
>>> colormap.rgb_bytes_tuple(0)
(32767, 16383, 65279)
>>> colormap.rgba_floats_tuple(1)
(255, 128, 0, 1.0)

Expected behaviour (v0.7.2):

>>> from branca.colormap import LinearColormap
>>> colormap = LinearColormap(colors=[(128, 64, 255), (255, 128, 0)])
>>> colormap.colors
[(0.5019607843137255, 0.25098039215686274, 1.0, 1.0), (1.0, 0.5019607843137255, 0.0, 1.0)]
>>> colormap.rgb_bytes_tuple(0)
(128, 64, 255)
>>> colormap.rgba_floats_tuple(1)
(1.0, 0.5019607843137255, 0.0, 1.0)

This seems to be due to the internal _parse_color function that was broken in https://github.com/python-visualization/branca/commit/8a8a2141c13947f6afaaf65a8c29c4417cd3a5a3#diff-6886114fc8e4fd6197705978c768e1f49469e2455fb1c4a8efda26a7b11bfa0bL51.

Current behaviour (v0.8.0 v0.8.1):

>>> from branca.colormap import _parse_color
>>> _parse_color((128, 64, 255))
(128, 64, 255, 1.0)

Expected behaviour (v0.7.2):

>>> from branca.colormap import _parse_color
>>> _parse_color((128, 64, 255))
(0.5019607843137255, 0.25098039215686274, 1.0, 1.0)