bashcomp: try to load git comp first (fix #592)

Closes #1139, fixes #1100

Instead of per-request approach of invoking `client.requestURL()`
manually whenever we're constructing a request path, simply define the
`/api/v3` prefix when configuring the API root URL for `simpleApi` client.

Fix copy-pasta

The description for --head said it was the head branch instead of head branch.

Git Hub Enterprise requests should always include /api/v3 in the URL
in order to hit the correct API endpoint. The ci-status and release
commands were producing the wrong request URL. As result, an LDAP
authentication page was returned rather than the expected JSON. A
parsing error could be seen: "invalid character '<' looking for beginning
of value".

This commit changes the construction of the request URL for the
ci-status and release commands, making sure the existing client.requestURL
function is called. This makes sure the API request hits always hits the
right endpoint in Git Hub Enterprise.

The `create` and `remote` commands needs to infer the current project
name from the project's directory. Instead of using the current working
directory, which doesn't necessarily match the project's toplevel
directory, use `git rev-parse --show-toplevel` which also respects the
`-C` global flag setting.

Fixes #1105, closes #1114

Fixes #1125, closes #1126

Add `hub release download` command that downloads all assets.

Make tests more robust to various Locales.

Prompt for user when the config has a token but no user. Fixes #1007

Don't use octokit in GhLatestTagName.

Fixes #1105

For git commands that are extended by hub, such as `git remote`, the
final git command would get executed without the git global flags
provided when executing hub in the first place.

This most notably broke the usage of `-C <dir>` flag.

Big overhaul of `hub release` command

Filter project issues by assignee

* Use -a or --assignee to filter repo issues list by assignee
* Makes it easier to find pull requests and issues you've been
  assigned to address

Since TAG is provided as argument, the user already knows the tag name
and there's no need to include it (rather clumsily) in the output.