convenient creation of uint

SemanticVersion struct.

Additional documentation.

Repot Trie and split into mutable and immutable variants.

Repotted Trie module.

Conflicts:
	src/lib.rs
	src/rlp.rs
	src/triehash.rs

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.

TrieDB borrowed db