This change will fix two issues:
1. When CLI sets a flag to an empty value in Go, e.g. 0 as to Uint64, the flag will be skipped and never set correctly. This problem could be solved by using option "WithOverwriteWithEmptyValue" when merge two configs.
2. The default non-empty value in server config will be overwritten to an empty value after flag initialization. This problem is solved by explicitly providing default value to all flags that have a default value option.
Adding a script that can automatically generate markdown pages from bor
CLI, so we can avoid copy-pasting helper strings whenever a flag is created,
deleted, or modified.
CLI docs could be generated with command `make docs`.
