FIx typo in documentation

[yucombinator]

The use of the vertical bar seems to break the rendering of the table in the documentation here:
http://rapidjson.org/md_doc_schema.html

Seems like we can fix it by using html encoding for the vertical bars as described in this post:
http://stackoverflow.com/questions/17319940/how-to-escape-a-pipe-char-in-a-code-statement-in-a-markdown-table/17320389#17320389

[coveralls]

Coverage remained the same at 99.937% when pulling 48f8364 on icechen1:patch-1 into b4dae2b on miloyip:master.

[miloyip]

Thank you very much.