Add some comments to common package (#2216)

sdk/storage/azure-storage-common/inc/azure/storage/common/crypt.hpp

@@ -12,8 +12,18 @@
 
 namespace Azure { namespace Storage {
 
+  /**
+   * @brief The class for the CRC64 hash function which maps binary data of an arbitrary length to
+   * small binary data of a fixed length.
+   */
   class Crc64Hash : public Azure::Core::Cryptography::Hash {
   public:
+    /**
+     * @brief Concatenates another #Crc64 instance after this instance. This operation has the same
+     * effect as if the data in the other instance was appened to this instance.
+     *
+     * @param other Another #Crc64Hash instance to be concatenated after this instance.
+     */
     void Concatenate(const Crc64Hash& other);
 
     ~Crc64Hash() override = default;

sdk/storage/azure-storage-common/inc/azure/storage/common/storage_exception.hpp

@@ -13,12 +13,29 @@
 
 namespace Azure { namespace Storage {
 
+  /**
+   * @brief An exception thrown when storage service request fails.
+   */
   struct StorageException : public Azure::Core::RequestFailedException
   {
+    /**
+     * @brief Constructs a #StorageException with a message.
+     *
+     * @param message The explanatory string.
+     */
     explicit StorageException(const std::string& message) : RequestFailedException(message) {}
 
+    /**
+     * Some storage-specific information in response body.
+     */
     std::map<std::string, std::string> AdditionalInformation;
 
+    /**
+     * @brief Constructs a #StorageException from a failed storage service response.
+     *
+     * @param response Raw HTTP response from storage service.
+     * @return #StorageException.
+     */
     static StorageException CreateFromResponse(
         std::unique_ptr<Azure::Core::Http::RawResponse> response);
   };