better compact printing of Py

[cjdoris]

In an IO context with compact=true, force the output to be a single line by replacing newlines with spaces.

If also limit=true, then truncate to one screen-width of output (i.e. one line) instead of one screen-full.

This makes printing of complex Python objects inside Julia arrays much nicer, such as:

julia> [np.random.rand(3,4) for _ in 1:3, _ in 1:3]
3×3 Matrix{Py}:
 array([[0.79715113, 0.83654893, 0.3008 ... 0.93258346, 0.62550964, 0.26787152]])  …  array([[0.73059587, 0.40056331, 0.0894 ... 0.94392892, 0.46400378, 0.13055773]])
 array([[0.92264918, 0.72076772, 0.6071 ... 0.05808218, 0.83883545, 0.23057753]])     array([[0.45971939, 0.81343033, 0.1869 ... 0.70010399, 0.53587046, 0.76999567]])
 array([[0.7933009 , 0.31953895, 0.7579 ... 0.47164865, 0.29715604, 0.5934403 ]])     array([[0.20724639, 0.76885944, 0.2058 ... 0.52625401, 0.71134752, 0.29692726]])

instead of this mess:

julia> [np.random.rand(3,4) for _ in 1:3, _ in 1:3]
3×3 Matrix{Py}:
 array([[0.54419557, 0.39819626, 0.23586015, 0.53822676],
       [0.6720559 , 0.82561704, 0.47703638, 0.90532732],
       [0.72706845, 0.14721132, 0.3037623 , 0.9163008 ]])  …  array([[0.08410984, 0.82419775, 0.89974616, 0.26844754],
       [0.87755284, 0.85069728, 0.79350635, 0.99253124],
       [0.63162664, 0.94685745, 0.45472159, 0.31408651]])
 array([[0.39378457, 0.1088128 , 0.42487836, 0.62327642],
       [0.6925987 , 0.30756797, 0.47317789, 0.98626029],
       [0.25974422, 0.62635918, 0.02137454, 0.17354563]])     array([[0.28815445, 0.91965669, 0.22342196, 0.43744798],
       [0.21790796, 0.96728322, 0.07411956, 0.88815802],
       [0.70591267, 0.24503941, 0.35849102, 0.19174126]])
 array([[0.15277849, 0.4535507 , 0.36206123, 0.67342048],
       [0.74135781, 0.05503536, 0.49546308, 0.03800956],
       [0.50645603, 0.06412445, 0.44264083, 0.23803791]])     array([[0.59485512, 0.94669031, 0.48734943, 0.67408912],
       [0.20983381, 0.18483092, 0.67507395, 0.27513866],
       [0.51489021, 0.11395934, 0.19776963, 0.71910407]])

Alternative to #595. Partial fix for #361.