Support hybrid madatory free + aid grade (USA grade only for now)

[vnugent]

Grades for aid routes in Yosemite are usually expressed in the form: <mandatory free grade> + <A or C aid grade>

• The Nose: 5.9 C1

To do

• Support A and C aid grade
• Support Hybrid format: free + aid hybrid grades #169

Related: OpenBeta/openbeta-graphql#233

[musoke]

A general solution to this would allow for grading other routes that involve multiple disciplines. For example, alpine routes that require both ice and rock climbing.