add config of link checker

[flingjie]

Summary of Changes

1. use quiet mode, only list invalid links in result;
2. add config, replaces links starting with / with https://solana.com/docs/core/ when check;

#370

[mikemaccana]

Should this be merged into #370? We wanted the quiet mode in there. If you're responding to questions for that PR, just add the new commits to that PR, that we we can discuss everything in one place!