PropertySet#body_rtf throws exception

[mmmries]

I'm on mri 1.9.2-p290 and when I tried to use the propertyset#body_rtf I get: "NoMethodError: undefined method `rtfdecompr' for RTF:Module"

This appears to be a really easy fix because it is just a confusion between the two rtf.rb files in the repo. To fix the issue I changed line 252 of lib/mapi/property_set.rb to read: "@body_rtf = (Mapi::RTF.rtfdecompr rtf_compressed.read)# rescue nil)" because the decompression method is defined in the Mapi::RTF not the global RTF module.

[aquasync]

I decided to just move everything from RTF to Mapi::RTF - there wasn't really a clear separation between the two, and this will be less prone to top-level constant collision problems.