Rename *result* to finalize

[tarcieri]

Implements the API changes from:

RustCrypto/traits#161

The universal-hash crate now uses update and finalize nomenclature ala the Initialize-Update-Finalize (IUF) interface naming scheme.

[codecov-commenter]

Codecov Report

Merging #56 into master will not change coverage.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #56 +/- ##
=======================================
Coverage 68.50% 68.50% =======================================
Files 11 11 Lines 454 454 =======================================
Hits 311 311 Misses 143 143 

Impacted Files	Coverage Δ
ghash/src/lib.rs	85.71% <100.00%> (ø)
ghash/tests/lib.rs	100.00% <100.00%> (ø)
poly1305/src/lib.rs	88.88% <100.00%> (ø)
poly1305/tests/lib.rs	100.00% <100.00%> (ø)
polyval/src/lib.rs	42.10% <100.00%> (ø)
polyval/tests/lib.rs	100.00% <100.00%> (ø)

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