Makes node prioritization insertion-independent

[luislavena]

The order in which nodes were inserted into a tree might produce failures in lookup mechanism.

tree = Radix::Tree(Symbol).new
tree.add "/one/:id", :one
tree.add "/one-longer/:id", :two

result = tree.find "/one-longer/10"

# expected `true`
result.found? # => false

In above example, reversing the order of insertion solved the issue, but exposed the naive sorting/prioritization mechanism used.

This change improves that by properly identifying the kind of node being evaluated and compared against others of the same kind.

It is now possible to know in advance if a node contains an special condition (named parameter or globbing) or is a normal one:

node = Radix::Node(Nil).new("a")
node.normal? # => true

node = Radix::Node(Nil).new(":query")
node.named? # => true

node = Radix::Node(Nil).new("*filepath")
node.glob? # => true

Which helps out with prioritization of nodes:

• A normal node ranks higher than a named one
• A named node ranks higher than a glob one
• On two of same kind, ranks are based on priority

With this change in place, above example works as expected:

tree = Radix::Tree(Symbol).new
tree.add "/one/:id", :one
tree.add "/one-longer/:id", :two

result = tree.find "/one-longer/10"

result.found? # => true

Fixes #18

[luislavena]

is found