Update documentation

Sources/SemanticVersion/SemanticVersion.swift

@@ -15,13 +15,95 @@
 import Foundation
 
 
+/// `SemanticVersion` is a struct representing a software or project version according to ["Semantic Versioning"](https://semver.org).
+///
+/// Given a version number MAJOR.MINOR.PATCH, increment the:
+/// 1. MAJOR version when you make incompatible API changes,
+/// 2. MINOR version when you add functionality in a backwards compatible manner, and
+/// PATCH version when you make backwards compatible bug fixes.
+/// Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.
+///
+/// Once instantiated, you can query a `SemanticVersion` about its components:
+///
+/// ```swift
+/// let v123 = SemanticVersion(1, 2, 3)
+/// v123.isStable        // true
+/// v123.isPreRelease    // false
+/// v123.isMajorRelease  // false
+/// v123.isMinorRelease  // false
+/// v123.isPatchRelease  // true
+/// ```
+///
+/// You can also instantiate a `SemanticVersion` from a string
+///
+/// ```swift
+/// let v200 = SemanticVersion("2.0.0")!
+/// v200.isStable        // true
+/// v200.isPreRelease    // false
+/// v200.isMajorRelease  // true
+/// v200.isMinorRelease  // false
+/// v200.isPatchRelease  // false
+/// ```
+///
+/// `SemanticVersion` supports beta versions:
+///
+/// ```swift
+/// let v300rc1 = SemanticVersion("3.0.0-rc1-test")!
+/// v300rc1.isStable        // false
+/// v300rc1.isPreRelease    // true
+/// v300rc1.isMajorRelease  // false
+/// v300rc1.isMinorRelease  // false
+/// v300rc1.isPatchRelease  // false
+/// v300rc1.major           // 3
+/// v300rc1.minor           // 0
+/// v300rc1.patch           // 0
+/// v300rc1.preRelease      // "rc1-test"
+/// ```
+///
+/// `SemanticVersion` is `Comparable` and `Equatable`:
+///
+/// ```swift
+/// v123 < v200          // true
+/// SemanticVersion("2.0.0")! < SemanticVersion("2.0.1")!  // true
+/// // NB: beta versions come before their releases
+/// SemanticVersion("2.0.0")! > SemanticVersion("2.0.0-b1")!  // true
+/// v123 == SemanticVersion("1.2.3")  // true
+/// SemanticVersion("v1.2.3-beta1+build5")
+///     == SemanticVersion(1, 2, 3, "beta1", "build5")  // true
+/// ```
+///
+/// `SemanticVersion` is `Hashable`:
+///
+/// ```swift
+/// let dict = [         // [{major 3, minor 0, patch 0,...
+///     v123: 1,
+///     v200: 2,
+///     v300rc1: 3
+/// ]
+/// ```
+///
+/// `SemanticVersion` is `Codable`:
+///
+/// ```swift
+/// let data = try JSONEncoder().encode(v123)  // 58 bytes
+/// let decoded = try JSONDecoder().decode(SemanticVersion.self, from: data)  // 1.2.3
+/// decoded == v123  // true
+/// ```
+
 public struct SemanticVersion: Codable, Equatable, Hashable {
     public var major: Int
     public var minor: Int
     public var patch: Int
     public var preRelease: String
     public var build: String
 
+    /// Initialize a version.
+    /// - Parameters:
+    ///   - major: Major version number
+    ///   - minor: Minor version number
+    ///   - patch: Patch version number
+    ///   - preRelease: Pre-release version number or details
+    ///   - build: Build version number or details
     public init(_ major: Int, _ minor: Int, _ patch: Int, _ preRelease: String = "", _ build: String = "") {
         self.major = major
         self.minor = minor
@@ -33,6 +115,9 @@ public struct SemanticVersion: Codable, Equatable, Hashable {
 
 
 extension SemanticVersion: LosslessStringConvertible {
+
+    /// Initialize a version from a string. Returns `nil` if the string is not a semantic version.
+    /// - Parameter string: Version string.
     public init?(_ string: String) {
         let groups = semVerRegex.matchGroups(string)
         guard