Creates a properties map from environment variables and JVM system properties.

Environment variables are added to the map twice: once with direct string keys, then again with the string key converted to a symbol. This allows for bare symbols in the EDN to resolve.

System properties are then added as key/value pairs; the keys are always strings.

Finally, the provided properties are merged in and the result passed to readers.

Creates a map of readers:

• #dyn/prop
• #dyn/keyword
• #dyn/long
• #dyn/boolean
• #dyn/join

The properties are used when creating the #dyn/prop reader.