Small updates to comments in a couple of cases

Sources/GZip/GzipArchive.swift

@@ -93,7 +93,6 @@ public class GzipArchive: Archive {
      Data will be also compressed with Deflate algorithm.
      It will be also specified in archive's header that the compressor used the slowest Deflate algorithm.
 
-     If during compression something goes wrong `DeflateError` will be thrown.
      If either `fileName` or `comment` cannot be encoded with ISO Latin-1 encoding,
      then `GzipError.cannotEncodeISOLatin1` will be thrown.
 

Sources/GZip/GzipHeader.swift

@@ -60,11 +60,10 @@ public struct GzipHeader {
         guard magic == 0x8b1f else { throw GzipError.wrongMagic }
         var headerBytes: [UInt8] = [0x1f, 0x8b]
 
-        // Third byte is a method of compression. Only type 8 (DEFLATE) compression is supported
+        // Third byte is a method of compression. Only type 8 (DEFLATE) compression is supported for GZip archives.
         let method = pointerData.byte()
         guard method == 8 else { throw GzipError.wrongCompressionMethod }
         headerBytes.append(method)
-
         self.compressionMethod = .deflate
 
         let flags = pointerData.byte()

Sources/ZIP/ZipCommon.swift

@@ -19,6 +19,7 @@ class ZipCommon {
         static let cp437Available = CFStringIsEncodingAvailable(cp437Encoding)
     #endif
 
+    // TODO: As extension?
     static func getStringField(_ pointerData: DataWithPointer, _ length: Int, _ useUtf8: Bool) -> String? {
         if length == 0 {
             return ""