Request chaining through embedded Javascript

[shrsv]

Major change: Support request chaining through embedded Javascript interpreter goja.
Minor change: Remove dependency on httpie, and switch to fork of httpie-go.

Documentation updates explaining the new changes.

Addresses multiple issues:

1. How to make use of variable to remember the response and use it in subsequence command? #10
2. Use a Go-based HTTP Client or lib instead of HTTPie ? #12