Add missing sync command flags - #409

Resolves #3, resolves #365, fixes #397, fixes #416

Adding missing flags and following changes:

• sync command can use same validation methods with cp. Currently, it does not accept single object sync and other validation logic is exactly the same with cp command. I don't see any reason for not supporting this:

sync s3://bucket/source.go .

• Updated givenCommand() method to add flags to command string.

• Added e2e tests for --exclude, --raw and --no-follow-symlinks and unit tests for other flags

• Below flags are not tested:

sse
sse-kms-key-id
acl
cache-control
expires
force-glacier-transfer