更改、暴露了一些属性，适配了Warp_content等

[SeaSoon]

首先编码改成了u8，然后将pickview的一些属性暴露出来，例如最大最小文字，颜色，透明度等暴露成attrs中的属性值来让用户自定义，接着解决了width和height设置为Warp_content的时候pickerview全屏问题，设置了默认值，同时兼容fill_parent和自己设置大小。改动不算太大，更加自由了一些。

[gzu-liyujiang]

@SeaSoon 的Pull Requests的init()方法中获取XML里设置的width和height不太靠谱，只针对了dp、dip，无法应对px。可以考虑以下方式：

        ViewGroup.LayoutParams layoutParams = getLayoutParams();
        if (layoutParams == null) {
            layoutParams = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
        }
        int width = layoutParams.width;
        int height = layoutParams.height;

        final float scale = context.getResources().getDisplayMetrics().density;
        if (width == ViewGroup.LayoutParams.WRAP_CONTENT) {
            if (mMaxTextSize == 0) {
                mViewHeight = (int) (160 * scale + 0.5f);
                mViewWidth = (int) (80 * scale + 0.5f);
            } else {
                mViewHeight = (int) mMaxTextSize * 4;
                mViewWidth = (int) mMaxTextSize * 2;
            }
            useDefault = true;
        } else if (width == ViewGroup.LayoutParams.MATCH_PARENT) {
            useDefault = false;
        } else {
            mViewHeight = (int) (height * scale + 0.5f);
            mViewWidth = (int) (width * scale + 0.5f);
            useDefault = true;
        }