Changes to grammar

## Type of Issue
"attribute" (memory node) -> outputs a value

1. Add Value to grammar : "what is the distance between the cow and the house" (right now filters -> attribute -> linear extent). Value takes full agent memory as input and returns a value.
2. Attribute takes a particular memory and returns a value ("that cow")
2. comparator should perhaps be added as an output of an attribute
1. stop when cow has x > 5
3. input_left an attribute -> comparator is also an attribute
3. input_left is null -> wait 2 minutes and walk forward for 15 seconds (num seconds elapsed since event has occurred)
4.
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- [ ] Bug report (to report a bug)
- [ ] Feature request (to request an additional feature)
- [ ] Tracker (I am just using this as a tracker)
- [ ] Refactor request
- [ ] Documentation Ask

## Description

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## Current Behavior

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## Expected Behavior

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## Steps to reproduce

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## Links to any relevant pastes or documents

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## Checklist

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