Add examples for Golang

[swinslow]

Should start adding some examples of SPDX documents for Golang:

• simple example with just standard library
• example with vendored single third party dependency
• example with vendored transitive third party dependencies
• examples with each of the above, using Go modules instead of vendor/ directory

[swinslow]

Added example 5 for simple Hello World sample, essentially just a translation of the C version for example 2.

Added example 6 which extends example 5 by adding a separate SPDX document and Relationship details about the Go distribution and standard libraries used to build the example.

[goneall]

@swinslow @nishakm - do we need any more examples or should we close this?