DummyTqdmFile line buffering

[anntzer]

Only call tqdm.write (which inserts a newline) if
DummyTqdmFile.write is itself called with a string containing a
newline; otherwise buffer the rest of the string.

See changes in test_tqdm.py for the patterns this allows.

• I have marked all applicable categories:
  • exception-raising fix
  • visual output fix
  • documentation modification
  • new feature
• If applicable, I have mentioned the relevant/related issue(s)

Less important but also useful:

• I have visited the source website, and in particular
  read the known issues
• I have searched through the issue tracker for duplicates
• I have mentioned version numbers, operating system and
  environment, where applicable:

  import tqdm, sys
  print(tqdm.__version__, sys.version, sys.platform)

[codecov-io]

Codecov Report

Merging #960 (d649576) into devel (37094ed) will increase coverage by 0.08%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##            devel     #960      +/-   ##
==========================================
+ Coverage   84.34%   84.42%   +0.08%     
==========================================
  Files          24       24              
  Lines        1603     1618      +15     
  Branches      264      265       +1     
==========================================
+ Hits         1352     1366      +14     
  Misses        215      215              
- Partials       36       37       +1     

[anntzer]

kindly bumping.

[casperdcl]

@anntzer I just made a couple of small fixes - let me know if it works for you.

[anntzer]

Seems reasonable to me.