wpiutil: Add C++ libuv wrappers (#1166)

- Provide an EventLoopRunner to run uv::Loop on a separate thread.

- Add raw_ostream wrapper for uv::Buffer.

wpiutil/src/main/native/include/wpi/uv/Error.h

@@ -0,0 +1,51 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_WPI_UV_ERROR_H_
+#define WPIUTIL_WPI_UV_ERROR_H_
+
+#include <uv.h>
+
+namespace wpi {
+namespace uv {
+
+/**
+ * Error code.
+ */
+class Error {
+ public:
+  Error() : m_err(UV_UNKNOWN) {}
+  explicit Error(int err) : m_err(err) {}
+
+  /**
+   * Boolean conversion.  Returns true if error, false if ok.
+   */
+  explicit operator bool() const { return m_err < 0; }
+
+  /**
+   * Returns the error code.
+   */
+  int code() const { return m_err; }
+
+  /**
+   * Returns the error message.
+   */
+  const char* str() const { return uv_strerror(m_err); }
+
+  /**
+   * Returns the error name.
+   */
+  const char* name() const { return uv_err_name(m_err); }
+
+ private:
+  int m_err;
+};
+
+}  // namespace uv
+}  // namespace wpi
+
+#endif  // WPIUTIL_WPI_UV_ERROR_H_