rebase 12/02, use go1.16rc1 in make, remove ioutil, start switching to io/fs for file i/o

ioutil's contents are now in io and os.
Eventually jfa-go's files will be embedded in the binary with go1.16's
new embed feature. Using io/fs will provide abstraction for accessing
these files, and allow for both embedded and non-embedded versions.
Also, internal paths to things like email templates, etc. will be
prefixed with "jfa-go:" to indicate to use the app's own Filesystem
instead of reading the file normally. This also allows for custom files
to continue to be used as they are currently.

Makefile

@@ -43,7 +43,7 @@ ts-debug:
 	cp -r ts build/data/web/js
 
 swagger:
-	go get github.com/swaggo/swag/cmd/swag
+	go1.16rc1 get github.com/swaggo/swag/cmd/swag
 	swag init -g main.go
 
 version:
@@ -51,10 +51,10 @@ version:
 
 compile:
 	$(info Downloading deps)
-	go mod download
+	go1.16rc1 mod download
 	$(info Building)
 	mkdir -p build
-	CGO_ENABLED=0 go build -o build/jfa-go *.go
+	CGO_ENABLED=0 go1.16rc1 build -o build/jfa-go *.go
 
 compress:
 	upx --lzma build/jfa-go