update usage text

update readme, remove unused file

simplify tool

up is finding its use as a parallel, batched task-runner.

This large change decouples the inventory file from up. Instead of tags,
you'll now pass in comma-separated IPs, and you can use another tool
such as inv2ips to return those IPs from an inventory if you choose.

This also removes the idea of executing tasks only if some conditions
are met. Instead, use a shell script to check those conditions and run
up when those conditions pass.

The parser has been simplified a great deal with a new syntax, removing
the need for a lexer and more closely mirroring make.

The concept of passing Upfile content into up via stdin was a good one,
but in practice didn't work well alongside scripts which also required
stdin. Support for the stdin flag "-f -" has been removed.

Variable substitution is much improved, now replacing variables from
largest to smallest, so $s doesn't happen before $ssh.

up now behaves more similarly to make. It will run the first task by
default. The syntax has changed to `up -t {ips} {cmd}`, removing the
`-c` flag.

update license to openbsd isc

update module name

update module path, license from mit to isc

remove checksum calculations

fix import

update module path

fix prompt logic

remove empty go.sum

split out inventory, improve flags, allow reading from stdin

set go.mod to go1.13

display stderr output

fix install instruction

remove -x flag, add environment vars

update github.com/pkg/errors dependency

fix tests

stream stdout and stdin from commands

add 'all' limit, fix races

improve logic clarity in parser