[feat] Add Error Context to HTTP 400 errors (cloudflare#24)

* [feat] Add Error Context to HTTP 400 errors
* [build] Add Go 1.10.x to Travis CI config

[fix] Fix --fields flag for single field requests (cloudflare#18)

[feat] Support timestamp formats & sampling (cloudflare#16)

* Add the timestamp-format and sample flags to logshare-cli
* Add TimestampFormat and Sample to logshare.Options
* Default to the new endpoint in the library
* Remove the option to use the old endpoint via logshare-cli.

Make the received endpoint the default for logshare-cli (cloudflare#10)

Merge pull request cloudflare#8 from bschmoker/docs-example

docs: example for rate-limiting

Merge pull request cloudflare#4 from cloudflare/elithrar/fields

[feat] Add fields support

[feat] Add new /received endpoint as option

Fix version flag via missing ldflags

[doc] Remove completed TODOs.