1.) consisify between camelCase and under_scores. The camelCase style is preferred.
2.) Document the available options in the class constructor in the method docblock.
3.) documentation should use the 3rd person declarative rather than the 2nd person imperative in documentation. "Sets the foo" rather than "Set foo". See http://pear.php.net/manual/en/standards.sample.php
4.) consistify between single quoted strings and double quoted. Single-quoted is preferred.
5.) The regular expression has the punctuation characters hard-coded when it appears you can specify them in the constructor.
6.) Lines should be at most 85 characters long.
7.) consider only using mb_strlen(), mb_strtolower(), etc if the functions are avialable That way installations that don't have mb_string can still use the package.
8.) stripText() could be simplified by using a regular expression.
9.) Package doesn't generate any HTML. I recommend renaming to Text_Metadata or Text_MetaTags
10.) The use of the PHP license is discouraged. Consider BSD, Apache2 or MIT instead.
11.) try running the code through phpcs (PHP_CodeSniffer)
12.) Min PHP version in package.xml is too low. At least PHP 5 is required.
13.) This package is a great cantidate for unit testing. Consider adding some tests to the proposal.