Add maxDistance as an input parameter

[lyfsn]

No description provided.

[mcdee]

Thanks for this PR. It appears that it is causing some failures in tests, please could you take a look at these?

[lyfsn]

@mcdee
Hey, some failures in tests were caused by the maxDistance default value problem. If user use the command line normally, the default value will be bound to 1024 by the environment variable https://github.com/wealdtech/ethdo/pull/134/files#diff-6f22dfa39a49962182a03b04b7d994b24a9e2ed446d37ad812c5499aa8c33fe0R67 , but in unit tests, the default value in the environment variable does not work.

So, I changed the maxDistance default value in the process function, retaining the original 1024, and if a user passes the --maxDistance parameter, the parameter will override the default 1024.

There should be no failures in tests now.

[mcdee]

Looking good, thanks for the changes.