Break up into smaller, more manageable files. Store parts in a tree structure to preserve relationships.

[trb]

The project grew too big for the current structural approach, it's time to refactor it into different parts. Ideas so far:

• Introduce PartTree to manage parts
• Inherit from Zend-Part and add part-related stuff on that class (e.g. isEnvelopedEmail)
• Parser should only parse and return PartTree, not do anything that's related to content access
• Remove envelope-identification from flattenParts() function, use relation ship info from PartTree to identify the enveloped email