Consider renaming buildUrl and buildRelativeUrl functions

[fenok]

Current names are misleading because these functions don't generate full URLs. Instead, they generate URL parts which are called paths in React Router. There already are buildPath and buildRelativePath functions, but they actually generate pathnames, so they can also be renamed.

These are the possible renamings:

• buildUrl => buildPath
• buildRelativeUrl => buildRelativePath
• buildPath => buildPathname
• buildRelativePath => buildRelativePathname

It won't even be a breaking change, because buildUrl can be safely used instead of buildPath.

[fenok]

buildPathname and buildRelativePathname seem redundant, so it's better to simply have buildPath and buildRelativePath.