provide version variable to use in main.cpp

[trel]

https://github.com/irods/irods_client_s3_api/pull/125/files#diff-4e63c76ee16f6ffa00e678da80b43894b0aa6dad81d2730c227bf9ccc7753ee1

-    "$id": "https://schemas.irods.org/irods-s3-api/0.2.0/schema.json",
+    "$id": "https://schemas.irods.org/irods-s3-api/0.3.0/schema.json",

We would like to provide a variable here to prevent needing to update this string for every release.

_Originally posted by @trel in #125 (comment)

[korydraughn]

Defining the value of either of the following as a macro will get us there.

irods_client_s3_api/CMakeLists.txt

Lines 13 to 14 in 549543a

	set(IRODS_CLIENT_VERSION "0.2.0")
	set(IRODS_S3_API_VERSION "${IRODS_CLIENT_VERSION}")

The macro can be defined for the target which compiles main.cpp.