Automatically remove per-line indent for @example tag

`@example` tags written with indent are *more readable*
Also, some JSDoc-processors, such as YUIDoc, do *require* such indents (see: http://yui.github.io/yuidoc/syntax/index.html#example)
But in JSDoc3 such indents, repeating from line to line, are output as is, and it looks ugly :(

The point of my change is:
1. Get leading spaces or tabs from the first line of `@example` content, assuming them to be an indent of the whole block
2. Trim this indent off the beginning of each line of the current `@example` block
3. At point of this, add new `removesIndent` option in `@example` tag definition, and get its value when parsing document
4. Also correct unit-tests for `TagEg` (and copy function utility `trim` to use within tests)