Add tbls coverage

[k1LoW]

$ tbls coverage pg://postgres:pgpass@localhost:55432/testdb\?sslmode=disable -c testdata/test_tbls_postgres.yml
Table                       Coverage
All tables                  16.1%
 public.users               20%
 public.user_options        37.5%
 public.posts               35.3%
 public.comments            14.3%
 public.comment_stars       0%
 public.logs                12.5%
 public.post_comments       87.5%
 public.post_comment_stars  0%
 public.CamelizeTable       0%
 public.hyphen-table        0%
 administrator.blogs        0%
 backup.blogs               0%
 backup.blog_options        0%
 time.bar                   0%
 time.hyphenated-table      0%
 time.referencing           0%

[codecov]

Codecov Report

Merging #222 into master will decrease coverage by 0.72%.
The diff coverage is 75.80%.

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
- Coverage   69.23%   68.51%   -0.73%     
==========================================
  Files          20       21       +1     
  Lines        3514     3570      +56     
==========================================
+ Hits         2433     2446      +13     
- Misses        848      893      +45     
+ Partials      233      231       -2     

Impacted Files	Coverage Δ
output/config/config.go	50.00% <33.33%> (ø)
coverage/coverage.go	80.35% <80.35%> (ø)
datasource/datasource.go	21.45% <0.00%> (-13.74%)	⬇️

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