Fix message API documentation
Fix message API documentation

Fallout from reorganization earlier today. Also adds exceptions to
documentation.

hustxiaoc/tchannel,bunnyblue/tchannel,Zirpon/tchannel,i/tchannel,sasa233/tchannel,sasa233/tchannel,benfleis/tchannel,hustxiaoc/tchannel,benfleis/tchannel,savaki/tchannel,i/tchannel,bunnyblue/tchannel,savaki/tchannel,chenwenbin928/tchannel,benfleis/tchannel,i/tchannel,hustxiaoc/tchannel,chenwenbin928/tchannel,savaki/tchannel,Zirpon/tchannel,vanloswang/tchannel,RyanTech/tchannel,bunnyblue/tchannel,RyanTech/tchannel,vanloswang/tchannel,sasa233/tchannel,RyanTech/tchannel,Zirpon/tchannel,chenwenbin928/tchannel,vanloswang/tchannel