StdSim improvements for handling binary data

[tleonhardt]

The StdSim class now accepts the following additional arguments in it's __init__() initializer:

• encoding: str='utf-8'
• errors: str='replace'

Additionally, the following two methods were added to the StdSim class:

• getbytes(self) -> bytes
• readbytes(self) -> bytes

These should prevent errors and improve options when dealing with underlying binary data.

[codecov]

Codecov Report

Merging #564 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #564      +/-   ##
==========================================
+ Coverage   93.11%   93.13%   +0.01%     
==========================================
  Files          11       11              
  Lines        3110     3118       +8     
==========================================
+ Hits         2896     2904       +8     
  Misses        214      214

Impacted Files	Coverage Δ
cmd2/utils.py	98.56% <100%> (+0.08%)	⬆️

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