add image, volume, and instance types
format eC2.mli for readability
removed type annotations from parsing functions
merge s3 with master
add create_image function
fix create_image function
include AWS error (crudely)
aws errors: print code and message
code cleanup
lib_test/describe_regions.ml
add region type
merge with origin/master
update describe_regions test
describe regions filters (awkward but works)
export REGION env var
DescribeKeyPairs
rename Field module to Util
comments/organization
update test
add DescribeKeyPairs parsing fn