Install 遵循 Apache2 开源协议发布，并提供免费使用。
Apache Licence 是著名的非盈利开源组织 Apache 采用的协议。该协议和 BSD 类似，
鼓励代码共享和尊重原作者的著作权，允许代码修改，再作为开源或商业软件发布。需要满足的条件：
1． 需要给代码的用户一份 Apache Licence ；
2． 如果你修改了代码，需要在被修改的文件中说明；
3． 在延伸的代码中（修改和有源代码衍生的代码中）需要带有原来代码中的协议，
商标，专利声明和其他原来作者规定需要包含的说明；
4． 如果再发布的产品中包含一个 Notice 文件，则在 Notice 文件中需要带有本协议内容。
你可以在 Notice 中增加自己的许可，但不可以表现为对 Apache Licence 构成更改。
具体的协议参考：http://www.apache.org/licenses/LICENSE-2.0
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
