Added project settings for Eclipse IDE
Rewrite message.c, add several features, other changes

Rewrite message.c

  - Use MimeMultiPart structure to construct a MIME message
  - It will make multi-level multipart possible (recursive)
  - Easy to manage the boundaries of multipart message
  - Easy to composing the message
  - createPlainEmail & createGpgEmail are not separated now

Add features

- Now we can send plain text message with an alternative HTML message (ContentType: multipart/alternative)
  Example:
  <code>echo "plain text" | email -s "plain text + HTML" -alt-html a-HTML-file.html someone@some-company.com</code>
- Now we can *embed* images into HTML message (ContentType: multipart/related)
  Example:
  <code>echo "See the image:<img src='linux.png'/>" | email -html -s "HTML with embedded image" -attach-related linux.png someone@some-company.com</code>
- Note: multipart/alternative and multipart/related can be used
  together, they can be used with or without encryption/signature too

Other changes

- Data transparency is now processed after MimeMessage printed, this
  will not break the data integrity when encrypt/sign a message
- Add some options in email.c, but not all of them are implemented, see
  TODO

TODO

- Auto detect character set of input (subject, body, recipients name...)
- Use a variable instead of utf-8 to encode a string/word

Warning

This commit does not well tested, may have potential bugs (memory leaks)