git apis (get html rendered from markdown and get raw content)

[rxjs-space]

api url:
https://api.github.com/repos/${username}/${reponame}/contents/${pathToFile}?ref=master
use api url withheader to get html rendered from markdown:
Accept:application/vnd.github.v3.html+json
Without that header, only the meta data will be returned.
example: https://api.github.com/repos/rxjs-space/files/contents/README.md?ref=master

raw url:
https://raw.githubusercontent.com/${username}/${reponame}/master/${pathToFile}
example: https://raw.githubusercontent.com/rxjs-space/files/master/README.md