Use singleton for Parameter

```
com.truemesh.squiggle.Parameter should have a method getInstance() that would
always return the same Parameter instance, so that we don't have to create a
new one everytime we use it.

Since parameter is stateless, there won't be a problem in sharing the instance.

Attached is the simple path to Parameter.java to achieve this.
```

Original issue reported on code.google.com by `brunoabdon` on 5 Aug 2010 at 8:28

Attachments:
- [diff-Parameter.java](https://storage.googleapis.com/google-code-attachments/squiggle-sql/issue-14/comment-0/diff-Parameter.java)

Start with com.truemesh.squiggle.Parameter in Parameter.java and review the attached diff-Parameter.java. Confirm the class is stateless and determine how callers currently create it. Done means getInstance() consistently returns the same Parameter instance without breaking existing usage.

Written by the indexing model from the issue text.