Make mods public in lib.rs

[mikedotexe]

There are mods like transactions, contract, account… which contain useful information to use for folks integrating. Real quick PR to make those public, since I saw this error:

[akorchyn]

You don't need that struct. It's intermediate builder. Use
Transaction::construct(..)

[frol]

@akorchyn I would really love to have some useful entry point in the root of the crate and kill prelude. We only have a few structs, not a gazillion of them and no traits afaik. I'd love to open https://docs.rs/near-api/latest/near_api/ and see the menu similar to the one in near.cli.rs, so as a developer I can quickly identify my next step. Similar to https://docs.rs/near-api/latest/near_api/prelude/index.html, but maybe an even more slimmed-down one.

[akorchyn]

If you don't mind I would keep them private for now. Not sure if it's necessary.
But if you think that it might bring more value to have everything pub, I would love to hear that :)