description text within backticks is blindly executed

#### To report a bug...

* What command(s) did you run?
`tasksh> start 34`

* What did you expect to happen?
the task would start

* What actually happened?
the task started, and it reported that it had attempted to run sections of the description contained within backticks

```text
tasksh> /rancher/
[task /rancher/]

ID Age Project Tag Description Urg
34 9d Personal IT ansible change `server` group to `rancher_server` and clean up old use of 1.95
`rancher_server`

1 task
There are local changes. Sync required.
tasksh> start 34
[task start 34]
sh: server: command not found
sh: rancher_server: command not found
sh: rancher_server: command not found
Starting task f275c6e1 'change `server` group to `rancher_server` and clean up old use of `rancher_server`'.
Started 1 task.
Tracking IT Personal ansible "change group to and clean up old use of"
Started 2018-05-21T12:22:00
Current 00
Total 0:00:00
You have more urgent tasks.
Project 'Personal' is 51% complete (53 of 109 tasks remaining).
tasksh> done 34
[task done 34]
sh: server: command not found
sh: rancher_server: command not found
sh: rancher_server: command not found
Completed task f275c6e1 'change `server` group to `rancher_server` and clean up old use of `rancher_server`'.
Completed 1 task.
Recorded IT Personal ansible "change group to and clean up old use of"
Started 2018-05-21T12:22:00
Ended 48:40
Total 0:26:40
You have more urgent tasks.
The project 'Personal' has changed. Project 'Personal' is 52% complete (52 of 109 tasks remaining).
```

## Details

I write everything in markdown, so it's common for me to use backticks in descriptions to block out words/commands/code. I've only been using tasksh for one day, and today it did the stuff I've detailed above. The easy answer is to say, "don't use backticks," but I think that it's worth reporting that anything in backticks is blindly executed when starting the task.

In a worst-case scenario, this means that a task with a description like ```make sure that `rm -fr ~` doesn't actually delete my home directory``` will do nasty and unexpected things.

Some of the output is from Timewarrior, which had the backticked "commands" removed before time tracking started. I don't know if this is a problem specifically within tasksh, Taskwarrior or Timewarrior.