Implement human-friendly memory request handling

[standage]

Supports raw numbers and scientific notation (as before), but now also supports common suffixes.

• 1K: 1000 bytes (1 KB)
• 700m: 700,000,000 bytes (700 MB)
• 16G: 16,000,000,000 bytes (16 GB)
• 1.3T: 1,300,000,000,000 bytes (1.3 TB)

Upper- and lower-case single-letter suffixes are supported. I'd prefer to update the documentation after #1396 is merged.

---

• Is it mergeable?
• make test Did it pass the tests?
• make clean diff-cover If it introduces new functionality in
  scripts/ is it tested?
• make format diff_pylint_report cppcheck doc pydocstyle Is it well
  formatted?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Is it documented in the ChangeLog?
  http://en.wikipedia.org/wiki/Changelog#Format
• Was a spellchecker run on the source code and documentation after
  changes were made?
• Do the changes respect streaming IO? (Are they
  tested for streaming IO?)
• Is the Copyright year up to date?

[codecov-io]

Current coverage is 90.88%

Merging #1397 into master will increase coverage by 0.01%

@@             master      #1397   diff @@
==========================================
  Files            57         57          
  Lines          7224       7239    +15   
  Methods           0          0          
  Messages          0          0          
  Branches        433        434     +1   
==========================================
+ Hits           6564       6579    +15   
  Misses          594        594          
  Partials         66         66          

Powered by Codecov. Last updated by 1fa14a3...5a94693

[ctb]

uncovered by test

[ctb]

Nice work! LGTM once you add test coverage.

[standage]

Additional test coverage.

[ctb]

thx!