Suppress validation errors on symbols in inline codes

[takahi-i]

I would like to skip errors on symbols in inline code blocks.

For the handling, I will add flags on tokens for inline blocks.

https://github.com/redpen-cc/redpen/blob/master/redpen-core/src/main/java/cc/redpen/tokenizer/TokenElement.java

[takahi-i]

I will take this!