Declare fields and methods starting with _ as private

[alcuadrado]

This was tried in ethereumjs/ethereumjs-blockchain#98, but it breaks some tests. We should fix those to be able to declare private fields/methods properly.

Once that's done, their @hidden tsdoc tags should be removed.

[alcuadrado]

I tried to fix this, but I'm not familiar enough with this library to make the required changes.

In particular, the logic around Blockchain.prototype._heads confusing and pretty undocumented.

If someone could point me to other projects consuming this library I may be able to document it and fix this.

[holgerd77]

@vpulim Do you have got some hints here?

[vpulim]

heads and the iterator function were around before I re-factored things to support Geth DBs. As far as I can tell, the purpose of Blockchain.prototype._heads is to keep track of and persist to disk the various block hashes used by the Blockchain.prototype.iterator() method. There is a separate hash for each unique name that is passed into the iterator() call.

This may be a good time to propose redo-ing the entire Blockchain class from scratch (if someone has the time). The legacy architecture is very hard to understand and makes it hard for contributors to make changes. This is probably the result of trying to have the Blockchain class do too many things. It should probably be split into multiple classes as @s1na proposed a while ago.

[jochem-brouwer]

Linking #895

EDIT: this PR has now moved to #930