Go modules support

[philtay]

Could you please add go.mod and go.sum files in the repository root? Thanks!

[jamie-digital]

Also some tests currently fail when using module mode:

--- FAIL: TestRuntimeStackTrace (0.00s)
    panic_test.go:115: 
        	Error Trace:	panic_test.go:115
        	            				panic_test.go:101
        	Error:      	Not equal: 
        	            	expected: "/Users/[redacted]/pkg/mod/github.com/aws/aws-lambda-go@v1.10.0/lambda/panic_test.go"
        	            	actual  : "github.com/aws/aws-lambda-go@v1.10.0/lambda/panic_test.go"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-/Users/[redacted]/pkg/mod/github.com/aws/aws-lambda-go@v1.10.0/lambda/panic_test.go
        	            	+github.com/aws/aws-lambda-go@v1.10.0/lambda/panic_test.go
        	Test:       	TestRuntimeStackTrace
FAIL
FAIL	github.com/aws/aws-lambda-go/lambda	0.028s