We should be _resolving_ symlinks (sometimes, still need to figure out when to
do this WRT IPNS). However, that's a larger feature.

1. Require files to have known sizes. We can add support for unknown sizes
_later_ but we can't use ServeContent for those files.
2. Replace the `sizeReadSeeker` with a `lazySeeker`. This one makes no
assumptions about how it's used so we're less likely to run into weird bugs.

Fixes symlink sizes.

daemon: support unix domain sockets for the API/gateway

docs: guide users to the right locations for questions

docs: readme improvements

Co-Authored-By: Eric Ronne <eric@protocol.ai>

docs: link remaining docs available, guide people to the right locations

docs: fix broken url

We no longer spit out the annoying http error.

All the work was client-side. Unix domain socket multiaddrs already worked
server-side.

fixes #4218

add systemd support

Update go-libp2p-http (and go-libp2p-gostream)

feat: add ipfs version info to prometheus metrics

Adds `ipfs_info` prometheus metric with version and commit info

```prometheus
ipfs_info{commit="9ea7c6a1-dirty",version="0.5.0-dev"} 1
```

This follows the same pattern as go and other systems, adding a gauge metric that is set to 1, with the version info addeds as labels.

This is a common pattern for prometheus. It lets operators merge version info into other prometheus metrics by multiplying it with the other stat, as described in https://www.robustperception.io/exposing-the-software-version-to-prometheus

For example, we already expose the go version info as

```prometheus
go_info{version="go1.12.9"} 1
```

License: MIT
Signed-off-by: Oli Evans <oli@tableflip.io>

Fix typo

Manually removed some newly-appeared // indirect imports as
they seem to just pollute the go.mod.

That way, we can reliably know when the daemon is ready.

Instead of letting systemd override the configured addresses, merge them. This
is likely the "expected" behavior.

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

chore(dep): update everything