feat: support EXTISM_ENABLE_WASI_OUTPUT (#51)

for any program that embeds the Go SDK, 

```sh
EXTISM_ENABLE_WASI_OUTPUT=1 extism call code.wasm foo --wasi 
will print things from e.g. fmt.Println (to stdout or stderr as needed)
```

brings the SDK into parity with the Rust runtime which has the same
behavior.

---------

Co-authored-by: zach <zach@dylibso.com>

extism.go

@@ -365,6 +365,11 @@ func NewPlugin(
 	// See: https://github.com/extism/go-sdk/pull/1#issuecomment-1650527495
 	moduleConfig = moduleConfig.WithStartFunctions().WithFSConfig(fs)
 
+	_, wasiOutput := os.LookupEnv("EXTISM_ENABLE_WASI_OUTPUT")
+	if c.hasWasi && wasiOutput {
+		moduleConfig = moduleConfig.WithStderr(os.Stderr).WithStdout(os.Stdout)
+	}
+
 	// Try to find the main module:
 	//  - There is always one main module
 	//  - If a Wasm value has the Name field set to "main" then use that module

plugins/println/go.mod

@@ -0,0 +1,10 @@
+module github.com/extism/extism-sdk-plugins-println
+
+go 1.21.0
+
+toolchain go1.21.1
+
+require (
+	github.com/extism/go-pdk v1.0.0-rc2 // indirect
+	github.com/valyala/fastjson v1.6.3 // indirect
+)

plugins/println/go.sum

@@ -0,0 +1,8 @@
+github.com/extism/go-pdk v0.0.0-20230119214914-65bffbeb3e64 h1:IfR1k741q+yQLvv5sLShCkvt3FgKU4wQVJfp7hhb/iY=
+github.com/extism/go-pdk v0.0.0-20230119214914-65bffbeb3e64/go.mod h1:1wdiAoG8306g4WK+6laBrS+75089/0V4XRVTllt8b5U=
+github.com/extism/go-pdk v1.0.0-rc1.0.20231019212020-62d54a6e0263 h1:uSo+K1JhsMlamDmaxyAGj0dGExZHLsL+Edyug0dC+uk=
+github.com/extism/go-pdk v1.0.0-rc1.0.20231019212020-62d54a6e0263/go.mod h1:Gz+LIU/YCKnKXhgge8yo5Yu1F/lbv7KtKFkiCSzW/P4=
+github.com/extism/go-pdk v1.0.0-rc2 h1:EZuo8idErnV8KB8TTSTiO2T1lkX047OQ7K8STjn2WBs=
+github.com/extism/go-pdk v1.0.0-rc2/go.mod h1:Gz+LIU/YCKnKXhgge8yo5Yu1F/lbv7KtKFkiCSzW/P4=
+github.com/valyala/fastjson v1.6.3 h1:tAKFnnwmeMGPbwJ7IwxcTPCNr3uIzoIj3/Fh90ra4xc=
+github.com/valyala/fastjson v1.6.3/go.mod h1:CLCAqky6SMuOcxStkYQvblddUtoRxhYMGLrsQns1aXY=

plugins/println/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+
+	pdk "github.com/extism/go-pdk"
+)
+
+//export run_test
+func run_test() int32 {
+	input := pdk.InputString()
+	fmt.Println("this was printed from the plugin", input)
+	return 0
+}
+
+func main() {}