Added terms functionality for searching

[frg]

Added the functionality described in #5

[frg]

Matched option term will highlight the entire option and by default will style the test as italics.

[frg]

Terms can be assigned to options by assigning the terms property with an array of strings.

VirtualSelect.init({
  ele: '#sample-select',
  options: [
    { label: 'Options 1', value: '1', terms: ['london', 'england'] },
    { label: 'Options 2', value: '2' },
    { label: 'Options 3', value: '3' },
  ],
});