Modified 2.1 to accurately describe full members, not associate members.

Also notes that modifications to the list remain with the Executive; e.g. removal of members.
Removed 'automatic' from 2.1, modified it as voted at AGM 2013.

No longer specifies when the exec update the list of modifications, just that they do keep it.
Merge pull request #3 from bethc/2013-Amendment-2.1

2013 amendment 2.1