Before, loading a module would be guarded by an optional platform
condition. This made it possible to avoid loading and evaluating a
module if it did not support the host platform.
Unfortunately, this made it impossible to share a single configuration
between GNU/Linux and Darwin hosts, which some wish to do.
This removes the conditional load and instead inserts host platform
assertions in the modules that are platform specific.
Fixes#1906
This change makes the services created via the lieer module aware of the notmuch config created by the home-mangager notmuch module (which is stored in a non-standard location).
Without this change all the lieer services created by the lieer module failed for me, as they were unable to find the notmuch config.
Add 'services.lieer', which generates systemd timer and service units
to synchronize a Gmail account with lieer. Per-account configuration
lives in 'accounts.email.accounts.<name>.lieer.sync'.
