We are trying to make it so that what ever crate a user uses they see
the same module/type tree (if the module or type exists).
E.g., one can do either of these.
If they use `bitcoin`:
```
use bitcoin::{
amount, block, fee_rate, weight, merkle_tree, opcodes,
pow, script, sequence, transaction, witness,
};
```
Or if they use `primitives`:
```
use bitcoin_primitives::{amount, block, fee_rate, weight};
```
The above imports were tested and `amount` was found to be missing.
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