Refresh CI infrastructure

[carlobaldassi]

Switch from Travis to GitHub,
Also, update TagBot etc.

[codecov-io]

Codecov Report

Merging #105 (7788555) into master (5ccf782) will increase coverage by 9.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #105      +/-   ##
==========================================
+ Coverage   85.53%   94.68%   +9.15%     
==========================================
  Files           5        5              
  Lines        1293     1299       +6     
==========================================
+ Hits         1106     1230     +124     
+ Misses        187       69     -118     

Impacted Files	Coverage Δ
src/common.jl	86.84% <0.00%> (-4.59%)	⬇️
src/settings.jl	94.47% <0.00%> (+8.27%)	⬆️
src/parsing.jl	96.73% <0.00%> (+11.16%)	⬆️

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