Limit the number of bands printed in showing BandedMatrix

[jishnub]

After this,

julia> B = brand(Int8,20,20,7,7);

julia> show(B)
BandedMatrix(-7 => Int8[39, -124, 64, -114, -47, 76, -40, 35, -87, 82, 40, 104, 122], -6 => Int8[49, 3, 72, -83, 84, -89, 65, 11, 3, -81, -29, -54, -80, -24], -5 => Int8[-81, -63, 127, -6, -115, 76, -120, 38, 124, 116, -14, 113, 98, -12, 47], -4 => Int8[-5, 99, -41, 40, -62, 86, -15, -90, 42, -73, -5, -24, 28, 56, 108, -91]  …  4 => Int8[13, 125, -10, -125, -96, 87, -66, 46, 127, -44, -43, 52, -70, 13, -55, -109], 5 => Int8[119, 16, 117, 122, -35, -67, -73, 89, 31, 75, -12, 101, -47, -90, 57], 6 => Int8[107, -112, -77, -57, 16, 86, -62, 52, 48, -31, -61, 26, -19, -93], 7 => Int8[0, -12, 39, 123, 90, 121, -109, 68, 57, -110, -126, -119, -93])

Some of the bands are not printed (indicated by …), which often vastly reduces the number of lines displayed. After this PR, at most 8 bands are printed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ff75189) 89.55% compared to head (f4cb6f1) 89.59%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
+ Coverage   89.55%   89.59%   +0.03%     
==========================================
  Files          25       25              
  Lines        3544     3556      +12     
==========================================
+ Hits         3174     3186      +12     
  Misses        370      370              

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