break API doc away from README.md

README.md was too long and unweildy

EC2.md

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+### EC2 API
+
+EC2 has two sets of APIs
+
+- One is a lower level API that directly maps onto Amazon's WSDL for the service.
+
+- The other is a simple API that provides limited functionality but with a a higher abstraction.
+
+### EC2 Simple API
+
+- Currently the following APIs are available:
+
+- ec2_terminate
+- ec2_launch
+- ec2_start
+- ec2_stop
+- ec2_show_status
+- ec2_get_hostnames
+- ec2_instances_by_tag
+- ec2_addprocs
+
+These are described [here](doc/ec2_simple.md)
+The source is in ```src/ec2_simple.jl```
+
+A generic API is ```ec2_basic```
+
+```ec2_basic(env::AWSEnv, action::String, params_in::Dict{Any, Any})``` just bundles the
+supplied params_in into an EC2 request. It is meant to be used while bugs, if any, in the
+advanced (generated) code exist for any of the APIs. Values in the params can be basic julia types,
+CalendarTime, Dict or an Array itself. Keys in the Dict MUST be same as those mentioned in
+the Amazon EC2 documentation for the corresponding action.
+
+### EC2 Advanced API
+
+
+Much of the boilerplate code is generated from the corresponding WSDL.
+For example, for the advanced API, the Julia types and functions are based on http://s3.amazonaws.com/ec2-downloads/ec2.wsdl
+
+Exported functions are in ```ec2_operations.jl```
+
+Types are defined in ```ec2_types.jl```
+
+Names and usage are similar to the AWS documentation http://awsdocs.s3.amazonaws.com/EC2/latest/ec2-api.pdf
+
+Each of the EC2 "actions" have a corresponding Julia function which takes in
+the appropriate Julia type.
+
+For example : ```RunInstances(env::AWSEnv , msg::RunInstancesType)``` (defined in ec2_operations.jl) where
+
+RunInstancesType (defined in ec2_types.jl) is
+
+```
+type RunInstancesType
+    imageId::Union(String, Nothing)
+    minCount::Union(Int32, Nothing)
+    maxCount::Union(Int32, Nothing)
+    ...
+
+    RunInstancesType(; imageId=nothing, minCount=nothing, maxCount=nothing, keyName=nothing, groupSet=nothing, additionalInfo=nothing, userData=nothing, addressingType=nothing, instanceType=nothing, placement=nothing, kernelId=nothing, ramdiskId=nothing, blockDeviceMapping=nothing, monitoring=nothing, subnetId=nothing, disableApiTermination=nothing, instanceInitiatedShutdownBehavior=nothing, license=nothing, privateIpAddress=nothing, clientToken=nothing, networkInterfaceSet=nothing, iamInstanceProfile=nothing, ebsOptimized=nothing) =
+         new(imageId, minCount, maxCount, keyName, groupSet, additionalInfo, userData, addressingType, instanceType, placement, kernelId, ramdiskId, blockDeviceMapping, monitoring, subnetId, disableApiTermination, instanceInitiatedShutdownBehavior, license, privateIpAddress, clientToken, networkInterfaceSet, iamInstanceProfile, ebsOptimized)
+end
+```
+
+Alternatively, the request can also be executed with the request type replaced by keyword arguments.
+
+For example ```For example : ```RunInstances(env, imageId="ami-xxxxxxxx", minCount=1)```
+
+
+
+Each of the functions returns an object of type:
+
+```
+type EC2Response
+    http_code::Int
+    headers
+    body::Union(String, Nothing)
+    pd::Union(LightXML.XMLElement, Nothing)
+    obj::Any
+end
+```
+
+In the event of an error, EC2Response.obj has an object of type
+
+```
+type EC2Error
+    code::String
+    msg::String
+    request_id::Union(String, Nothing)
+end
+```
+
+For succcessful requests, EC2Response.obj will contain an object of the appropriate type.
+
+For example, for RunInstances, the EC2Response.obj will be of type RunInstancesResponseType