Functions for getting script hashes

[Hrom131]

Describe the feature

Simplicityhl-std must have functions for conveniently obtaining script hashes for inputs and outputs

Functions for getting script hashes:

1. get_script_hash(index: u32, index_type: IndexType)
2. get_input_script_hash(index: u32)
3. get_output_script_hash(index: u32)

Dependencies

• Functions for retrieving the AssetId and Amount #32