Remove macos & windows from actions

Use a self-hoted runner for github actions

correct documentation

disable linter in github workflow (it fails unexpectedly)

move from .travis.yml to .github/workflow; use animated giv instead of webm

improve examples

Merge pull request #26 from logrusorgru/pull/25

bump v4; fix go.mod, add hyperlinks, configurations and flags examples

add changelog; bump v4

add hyperlink tests

improve tests coverage

combine color with configurations in the Value

user non-interface, non-pointer Value

refactor entire package (except tests); add hyperlinks feature

add methods to Color; add Colored interface; add special types ColorIndex and GrayIndex to avoid collisions