Add eval output type (nextflow-io#4493)

This PR introduces the output `eval` type that allows the definition of
a script expression that needs to be computed in the script context to evaluate
the output value to be emitted. An example would be:

```
process someTask {
  output:
  eval 'bash --version'
  '''
  some-command --here
  '''
}
```

Signed-off-by: Paolo Di Tommaso <paolo.ditommaso@gmail.com>
Signed-off-by: Ben Sherman <bentshermann@gmail.com>
Co-authored-by: Ben Sherman <bentshermann@gmail.com>
Co-authored-by: Dr Marco Claudio De La Pierre <marco.delapierre@gmail.com>

docs/process.md

@@ -1068,6 +1068,9 @@ The `stdout` qualifier allows you to output the `stdout` of the executed process
 ```
 
 <<<<<<< HEAD
+<<<<<<< HEAD
+=======
+>>>>>>> df978113c (Add eval output type (#4493))
 (process-out-eval)=
 
 ### Output type `eval`
@@ -1085,8 +1088,19 @@ Only one-line Bash commands are supported. You can use a semi-colon `;` to speci
 
 If the command fails, the task will also fail. In Bash, you can append `|| true` to a command to suppress any command failure.
 
+<<<<<<< HEAD
 =======
 >>>>>>> 21ea0ed2a (Update documentation (#4700) [ci skip])
+=======
+(process-set)=
+
+### Output type `set`
+
+:::{deprecated} 19.08.1-edge
+Use `tuple` instead.
+:::
+
+>>>>>>> df978113c (Add eval output type (#4493))
 (process-out-tuple)=
 
 ### Output type `tuple`