Add "text-summary" nyc reporter

[igor-toporet]

Also moved nyc configuration to .nycrc file.

Benefits (to me) are:

1. Test script got shorter
2. nyc configuration got centralized, becoming a default place for possible future additions/changes
3. Test output gets amended by a handy summary, e.g.

  78 passing (4m)

---------------|----------|----------|----------|----------|----------------|
File           |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
---------------|----------|----------|----------|----------|----------------|
All files      |    90.09 |    75.93 |    95.83 |    89.84 |                |
 bin           |    88.04 |    81.08 |    94.44 |    87.91 |                |
  help.js      |      100 |      100 |      100 |      100 |                |
  index.js     |      100 |      100 |      100 |      100 |                |
  main.js      |    84.93 |    76.67 |    92.86 |    84.72 |... 139,155,156 |
  version.js   |      100 |      100 |      100 |      100 |                |
 lib           |    90.63 |       75 |    96.15 |    90.35 |                |
  copy-sync.js |      100 |      100 |      100 |      100 |                |
  copy.js      |    87.32 |    69.23 |      100 |    86.36 |... 144,154,162 |
  cpx.js       |    89.66 |    71.09 |    93.62 |    89.45 |... 455,478,541 |
  index.js     |    89.66 |    86.11 |      100 |    89.66 |       42,43,95 |
  queue.js     |      100 |    83.33 |      100 |      100 |                |
---------------|----------|----------|----------|----------|----------------|

=============================== Coverage summary ===============================
Statements   : 90.09% ( 400/444 )
Branches     : 75.93% ( 183/241 )
Functions    : 95.83% ( 92/96 )
Lines        : 89.84% ( 389/433 )
================================================================================

[codecov-io]

Current coverage is 89.83% (diff: 100%)

Merging #26 into master will not change coverage

@@             master        #26   diff @@
==========================================
  Files             9          9          
  Lines           433        433          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits            389        389          
  Misses           44         44          
  Partials          0          0          

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[mysticatea]

Thank you!