Add more information to update marker file

In addition to the previously added package name / path, the marker file
now gets populated with the following:

- host name (redundant, but easy to parse from here)
- the time stamp when the update happened
- build commit
- build configuration

The encoding of the file is changed to be ASCII, otherwise PowerShell always
places the ugly BOM (byte-order-mark) at the beginning, confusing a lot of
editors.

Fixes #46