Additional work & convenience functions on crypto, bytes & hash.

Renaming mut_bytes() to as_slice_mut().

Secure trie functions & structs.

address to and from h256

convenient creation of uint

SemanticVersion struct.

Additional documentation.

Repot Trie and split into mutable and immutable variants.

Repotted Trie module.

heapsize && squeeze

decoding to rust array [T; $len] using macro

added H264 (required for extras_db slices), removed unnecessary unsafe code

Trie takes a reference to HashDB.