Use BLAS for pairwise sumabs2 when possible
Rename varzm_pairwise -> sumabs2_pairwise

Also some minor reorganization
Make splice!(::BitVector, ::Integer, ::BitVector) return a Bool

Previously this returned a new BitArray, which was inconsistent with
splice!(::Vector{Bool}, ::Integer, ::Vector{Bool})
Update style guide to point to FAQ on type parameters
Merge pull request #6979 from JuliaLang/sjk/bitsplice

Make splice!(::BitVector, ::Integer, ::BitVector) return a Bool
Merge pull request #6985 from JuliaLang/kms/doc_param_types

Update style guide to point to FAQ on type parameters
Merge pull request #6974 from JuliaLang/sjk/faster-sumabs2

Use BLAS for pairwise sumabs2 when possible