Reverse URL resolving should be public method

[hogart]

"Reverse URL resolving" means "converting name and params to URL string".

Right now there's only VueRouter#match method, which is great, but it's not documented, doesn't take base and mode into account, and doesn't normalize relative urls, so it's not really an equivalent of what's going inside <router-link> render method.

Rationale for making reverse URL resolving public is following:

• In isomorphic apps we may need to send some link via email, so we should be able to get this link as text
• Several kind of apps, (e.g. google drive, bit.ly) require to provide link which can be copied by user
• Issues like 2.0 doesn't respect target="_blank" attr #827 where <router-link> doesn't support some attribute will have simple work-arounds

[yyx990803]

resolved via merging #918