Fix typos (apple#222)

Author: rex4539

Guides/Keyed.md

@@ -71,7 +71,7 @@ Calling `keyed(by:)` is an O(_n_) operation.
 
 #### Alternative names
 
-Kotlin's `associatedBy` naming is a good alterative, and matches the past tense of [Swift's API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/), though perhaps we'd spell it `associated(by:)`.
+Kotlin's `associatedBy` naming is a good alternative, and matches the past tense of [Swift's API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/), though perhaps we'd spell it `associated(by:)`.
 
 #### Customization points
 

Sources/Algorithms/Documentation.docc/MinAndMax.md

@@ -16,7 +16,7 @@ or a specific number of elements at the minimum and maximum.
 - ``Swift/Sequence/max(count:sortedBy:)``
 - ``Swift/Collection/max(count:sortedBy:)``
 
-### Finding the Minimum and Maximum Elements Simulataneously
+### Finding the Minimum and Maximum Elements Simultaneously
 
 - ``Swift/Sequence/minAndMax()``
 - ``Swift/Sequence/minAndMax(by:)``

Sources/Algorithms/Split.swift

@@ -512,7 +512,7 @@ extension SplitCollection: Collection {
     var subsequenceStart = i.baseRange.upperBound
     if subsequenceStart < base.endIndex {
       // If we're not already at the end of the base collection, the previous
-      // susequence ended with a separator. Start searching for the next
+      // subsequence ended with a separator. Start searching for the next
       // subsequence at the following element.
       subsequenceStart = base.index(after: i.baseRange.upperBound)
     }