support multi-color in tab

patch for [How to make Title pager with two color text?](https://github.com/astuetz/PagerSlidingTabStrip/issues/146)
Use Spanned string for TextView to support different color in TextView:
##### Step one: Disable capital；

	app:pstsTextAllCaps="false" 


##### Step two: Use html to set different color；

	public class MyPagerAdapter extends FragmentPagerAdapter {

		private final String[] TITLES = { "Categories <font color='red'>1</font>", "Home <font color='red'>2</font>", "Top Paid", "Top Free", "Top Grossing", "Top New Paid",
				"Top New Free", "Trending" };

		public MyPagerAdapter(FragmentManager fm) {
			super(fm);
		}

		@Override
		public CharSequence getPageTitle(int position) {
			return Html.fromHtml(TITLES[position]);
		}

		@Override
		public int getCount() {
			return TITLES.length;
		}

		@Override
		public Fragment getItem(int position) {
			return SuperAwesomeCardFragment.newInstance(position);
		}

	}