print what asv gh-pages is doing to the console

I just ran `asv gh-pages` for the first time (I think) and it printed exactly the same as `asv publish` to the console:
```
$ asv publish
[ 20.00%] · Loading machine info
[ 40.00%] · Loading results..
[ 60.00%] · Generating graphs........
[ 80.00%] · Getting tags
[ 80.00%] ·· Fetching recent changes...
[100.00%] · Writing index
$ asv gh-pages
[ 20.00%] · Loading machine info
[ 40.00%] · Loading results..
[ 60.00%] · Generating graphs........
[ 80.00%] · Getting tags
[ 80.00%] ·· Fetching recent changes...
[100.00%] · Writing index.
```

Apparently it did commit to a `gh-pages` branch though and push it out to Github.
It would be nice if it printed some info to the console that it's doing this (or print the `git` commands it executed).