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

Refers to #5

Refers to #5

Report if the service account is not a member of the local group
"Performance Monitor Users" when the service binaries are being updated.

Refers to #40

Fixes #5

Refers to #5

Important if it has already been removed before, otherwise the updater
would stop at this point.

- config validation
- reporting
- log file upload
- update-source folder structure
- permissions

Fixes #33

An exception would otherwise result in a silenced error as the output
would be discarded.

Fixes #30

Using this option will shut down the service independent of its state,
remove the status XML file (will be re-created by the service during
the next start) and (re-) starts the service no matter if it was running
before.

There is no real benefit from having those configurable as all other
parts of the solution have those paths hardcoded relative to the
installation directory of the service.

Refers to #18

Closes #28

Refers to #18, #28

Refers to #18, #28

Refers to #28

This way we can handle the situation in the calling code, e.g. sending
an email notification to the admin address.

Locating the update package is now done in Find-InstallationPackage and
stored in $UpdPackage, so we can safely remove the redundant code. In
addition, this change makes the function return $True or $False,
depending if the copy action succeeded.

Refers to #28

Refers to #18, #28

After validating the config files we can now safely trigger the update
if necessary.

Refers to #18, #28

No checks are done in Update-Configuration any more, as the control
logic has been changed to do those beforehand now. Therefore also
Update-File is not comparing the write-times any more nor terminating
the script if something fails (now returning $False instead).

Refers to #18, #28

Instead of terminating the entire script immediately we log a message
and pass on success / fail so the remaining script logic can deal with
the situation.

Refers to #18, #28

This adapts the updater to the new configuration locations (#18) and
changes the control flow so that first the script will detect if any
updates are necessary at all and then validate the configuration files
(respecting what parts will be updated), preparing for the actual update
tasks (as this is currently work-in-progress, those update tasks are
disabled for now.

Refers to #28

The updater should also check if an existing configuration that won't be
updated validates correctly with newer service binaries and stop the
process of updating if the check fails.

Refers to #28

Refers to #28

Refers to #18