Case insensitive search

[String#include?](http://www.ruby-doc.org/core-2.1.0/String.html#method-i-include-3F) is case sensitive, so search queries returned false negatives.  

```
$ glean search america

```

```
$ glean search --contrib units

```
          
By using a `Regexp`, search can be case insensitive.

```
$ glean search america
naics-codes -- NAICS (North American Industry Classification System) codes
us-states -- The United States of America
```

```
$ glean search --contrib units
jonmagic/units_of_measurement -- Units of measurement: Units of measurement in popular systems
```