Performance improvements

[peteraisher]

Several improvements to the internals of _search(_:in:) to avoid the less efficient parts of Swift's String implementation, namely the fact that count is O(n) for a string of length n, and String.index(_, offsetBy: n) is also O(n).

Overall speedup of up to 2.5x for search operations.

FuseUtilities.swift:

• add a version of calculateScore which takes a patternLength parameter, to avoid repeated calls to String.count, which is O(n) for a string of length n.
• calculatePatternAlphabet: eliminate unnecessary loop zeroing mask by using nil coalescing instead.
• calculatePatternAlphabet: eliminate unnecessary calls to String.index(_, offsetBy: n), which is O(n), by instead looping through pattern.enumerated().
• findRanges: eliminate unnecessary variable end and unnecessary subtraction of one, using ..< instead of ... operator.

Fuse.swift:

• change all calls to calculateScore to use pattern.len (see FuseUtilities.swift)
• calculate text.count only once
• eliminate unnecessary Double/Int conversions in calculation of binMid
• avoid calls to text.char(at:), which is O(n+j) for offset of j in string length n, instead calculate index of currentLocation once, then apply String.index(before:) once per loop iteration, which is O(1).

String+Fuse.swift:

• avoid deprecated encodedOffset and instead compare self.count to position

[mthole-old]

Nice work!

[krisk]

Amazing work @peteraisher!

[peteraisher]

Thanks @krisk, glad you approve!