Update according to TODO

[kgryte]

• copy option
• accessor option
• Makefile
• README
• validation dependencies
• dev dependencies
• remove preamble
• update license info
• tests for code pathways
• dotfiles

Resolves compute-io/todo#40

NOTE: breaking change. add no longer mutates by default. This behavior must be explicitly set using the copy option. While memory management is important, three factors contribute to turning off mutation by default:

1. principle of least surprise: mutation is a source of bugs, especially when multiple operations may operate on the same data store. Reasoning about mutable objects as they travel through a program with black boxes (functions mutating state) is more complex.
2. consideration that, for object arrays, mutation has a side-effect that object elements are eliminated and replaced with numeric results. For more complex object arrays, this is unlikely to be desired. Setting {'copy':true} for each invocation is probably more than should be asked.
3. readability. If mutation is desired, having the invocation signature add( x, y, {'copy': false}) means that the code is explicit in describing the behavior. If I understand that the copy option pertains to mutation, then I derive meaning from the signature.

[coveralls]

Coverage remained the same at 100.0% when pulling 93d3355 on develop into 3ede407 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 93d3355 on develop into 3ede407 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling a5d30b3 on develop into 3ede407 on master.

[Planeshifter]

LGTM. I merge the pull request and then you can publish the update to npm.