composeAndExecute command that loads and executes over arbitrary transformer set exported from a go plugin generated according to config file; test for plugin generation, loading, and execution; work on plugins README

plugins/README.md

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+## Plugins
+
+This directory is for Exporter plugins (.go and .so files) generated by, output from, and linked to from the composeAndExecute command  
+These plugins are generated using information provided in a .toml config file 
+
+The config file requires, at a minimum, the below fields:
+
+```toml 
+[database]
+    name = "vulcanize_public"
+    hostname = "localhost"
+    user = "vulcanize"
+    password = "vulcanize"
+    port = 5432
+
+[client]
+    ipcPath = "http://kovan0.vulcanize.io:8545"
+
+[exporter]
+    filePath = "$GOPATH/src/github.com/vulcanize/vulcanizedb/plugins/"
+    fileName = "exporter"
+    [exporter.transformers]
+            transformer1 = "github.com/path/to/transformer1"
+            transformer2 = "github.com/path/to/transformer2"
+            transformer3 = "github.com/path/to/transformer3"
+```
+
+In the above, the exporter.transformers are mappings of import aliases to their import paths 
+If the individual transformers require additional configuration variables be sure to include them in the .toml file 
+
+The general structure of a plugin .go file, and what we would see with the above config is below   
+Note that `shared_transformer` is a reserved alias needed for the generic TransformerInitializer type:
+
+```go
+package main
+
+import (
+	shared_transformer "github.com/vulcanize/vulcanizedb/libraries/shared/transformer"
+	transformer1 "github.com/path/to/transformer1"
+	transformer2 "github.com/path/to/transformer2"
+	transformer3 "github.com/path/to/transformer3"
+)
+
+type exporter string
+
+var Exporter exporter
+
+func (e exporter) Export() []shared_transformer.TransformerInitializer {
+	return []shared_transformer.TransformerInitializer{
+		transformer1.TransformerInitializer,
+		transformer2.TransformerInitializer,
+		transformer3.TransformerInitializer,
+	}
+}
+```
+
+As such, to plug in an external transformer all we need to do is create a [package](https://github.com/vulcanize/maker-vulcanizedb/blob/compose_and_execute/pkg/autogen/test_helpers/bite/initializer.go) that exports a variable `TransformerInitializer` that is of type [TransformerInitializer](https://github.com/vulcanize/maker-vulcanizedb/blob/compose_and_execute/libraries/shared/transformer/transformer.go#L19)   
+As long as the imported transformers abide by the required interfaces, we can execute over any arbitrary set of them