add -h|--help command
infer CI settings from environment variables

- matches behavior of the official ruby coveralls gem

- remove doveralls.config
simply use an ISO 8601 extended date format
use hash tables and std.json

- instead of UDTs and medea
fallback for libgit2 using command line git

- to avoid libgit2 installation in CI environments
use libcurl for upload

- windows usually has no curl binary
- no need to write a file
- allow to configure endpoint via COVERALLS_ENDPOINT
add dump argument

- writes json report to stdout instead of uploading it
Merge pull request #1 from MartinNowak/master

major rework