Support comments in schema

[srfrog]

This PR adds support for comments in schemas. Comments begin with # and end with new line or when EOF is reached. A schema with only comments is treated as a no-op.

Example:

#
# This is a comment
#
user: bool .
user.name: string @index(exact) . # this should be unique
user.email: string @index(exact) . # this should be unique and lower-cased
user.password: password .
user.code: string . # for password recovery (can be null)
node: bool .
node.hashid: string @index(exact) . # @username/hashid
node.owner: uid @reverse . # (can be null)
node.parent: uid . # [uid] (use facet)
node.xdata: string . # store custom json data
#
# End of test
#

Example with type system:

# User is a service user
type User {
   # TODO: add more fields
   Name: string # e.g., srfrog
                # expanded comment
                # embedded # comments # here
}
# /User

Closes #3130

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This change is 

[manishrjain]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @srfrog)

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schema/state.go, line 111 at r1 (raw file):

// lexComment lexes a comment text.
func lexComment(l *lex.Lexer) lex.StateFn {

There's another func like this in gql/state.go. Can you move that func within lex pkg, and use that in both places?

[srfrog]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @manishrjain)

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schema/state.go, line 111 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

There's another func like this in gql/state.go. Can you move that func within lex pkg, and use that in both places?

They are named the same but don't work the same. This one is specific to schema lexText function and needs newlines emitted. I will rename this one to lexTextComment to remove ambiguity.

[manishrjain]

Thanks for taking care of this quickly.

Reviewed 2 of 3 files at r1, 1 of 1 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @manishrjain)