Add spec templates
Add specs for Disk#read and Disk#index
Start specs for Disk#subsource
Add specs for Disk#subsource and Disk#close
Add specs for Rex::ImageSource::Memory#initialize
Add first specs for Rex::ImageSource::Memory#read
Finish examples for Memory#read
Add specs for Memory#close
Add specs for Memory#subsource
Add specs for Memory#index
Add specs for #read_asciiz and fix bugs there
Add shared examples
Fix grammar
Land #3846, Rex::ImageSource specs