Add clipboard copy (-c) to browse command

Fix <USER> in usage string

The -c parameter will put the url into the clipboard instead of
opening in the browser.

Since we're no longer connected to a tty, we can't start up tmux.

Add --set-upstream to git push commands.

This ensures that a branch pushed using "hub pull-request" has its
upstream branch set to the target of the push.

We might bring back the self-updater at some point, but right now it's
dead code and it's not clear to me how to implement it in a fashion
where it also updates dependent files such as shell completion scripts
and man pages.

Use --cmd instead of -c to set default filetype for vim

Always start template lookup from the toplevel directory of the repo.

Fixes #1242

Closes #1332, fixes #1305

This prevents it from showing up under custom commands in `hub help -a`

Check if config location is writeable before authenticating

If file is not present before checking for writing, remove it after check.
Add test to check for writeability in default location

Fixes #1314

Fixes #1320

Since `--push` has just created a new branch, there could be a slight
delay before GitHub registers it, and there's a possibility that a 422
would be returned for the "head" field. If that happens, retry the POST
a couple of times until it either succeeds or times out.

don't copy .txt files to man path

Fix typo

compliation -> compilation

 on each man hub* commands in the shell, the shell reports
 warning: ignore bogus filename for the respective .txt present
 in the man path.

 copying only the man file to the man path solves this issue.

This removes an extra step from the process of publishing a pull
request. It also gives the user a chance to back out of the entire
process by saving an empty pull request message.

Installs hub binary and man pages into `/usr/local` by default.

Fixes #1291

Otherwise, for example, a `browse` command would have failed silently if
the program for the browser couldn't be found.

Ref. f507de05

Fixes #1289

Ref. #1289

Fixes #1293