Update Travis & Codecov support, update README.md

[fingolfin]

BTW, I find it confusing that there are both a README and a README.md. Perhaps they should/could be merged?

[codecov]

Codecov Report

Merging #17 into master will increase coverage by 4.81%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #17      +/-   ##
==========================================
+ Coverage   74.16%   78.97%   +4.81%     
==========================================
  Files          22       44      +22     
  Lines        7322     8882    +1560     
==========================================
+ Hits         5430     7015    +1585     
+ Misses       1892     1867      -25

Impacted Files	Coverage Δ
gap/affine.gd	100% <0%> (ø)
gap/catenary-tame.gd	100% <0%> (ø)
gap/good-ideals.gd	100% <0%> (ø)
gap/affine-def.gd	100% <0%> (ø)
gap/operations.gd	100% <0%> (ø)
gap/dot.gd	100% <0%> (ø)
gap/numsgps-utils.gd	100% <0%> (ø)
gap/numsgp-def.gd	100% <0%> (ø)
gap/ideals-def.gd	100% <0%> (ø)
gap/random.gd	100% <0%> (ø)
... and 34 more

[fingolfin]

That code coverage increased is not due to this PR, but rather due to a change we just merged to GAP itself: gap-system/gap#2772

[pedritomelenas]

Thanks for the changes, @fingolfin

[pedritomelenas]

We should delete probably README...