Add example for buffered access when reading from a file

[dralley]

No description provided.

[codecov-commenter]

Codecov Report

Merging #438 (33b6e6d) into master (d8ae1c3) will decrease coverage by 0.06%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master     #438      +/-   ##
==========================================
- Coverage   51.20%   51.13%   -0.07%     
==========================================
  Files          25       26       +1     
  Lines       13283    13308      +25     
==========================================
+ Hits         6801     6805       +4     
- Misses       6482     6503      +21     

Flag	Coverage Δ
unittests	51.13% <16.66%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
examples/read_buffered.rs	0.00% <0.00%> (ø)
src/reader/buffered_reader.rs	65.68% <100.00%> (+0.62%)	⬆️
src/reader/slice_reader.rs	100.00% <100.00%> (ø)
src/reader/mod.rs	90.48% <0.00%> (-0.11%)	⬇️
src/lib.rs	12.26% <0.00%> (-0.07%)	⬇️
src/de/mod.rs	75.16% <0.00%> (+0.09%)	⬆️
src/de/map.rs	72.35% <0.00%> (+0.46%)	⬆️

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