consider removing kmer/sequence type inference from strings in favor of generalized version in BioSequences

[cjprybol]

See current code at:

Kmers.jl/src/kmer.jl

Line 329 in f7a1328

@inline function Kmer(seq::String)

Rationale at: BioJulia/BioSequences.jl#268 (comment)

and candidate replacement capability at: BioJulia/BioSequences.jl#269