* Separate DB and metadata migrations
* Refactor Migrate.hs to generate list of migrations at compile-time
* Replace ginger with shakespeare to improve performance
* Improve migration log messages
* allow customizing GraphQL root field names, close#981
* document v2 track_table API in reference
* support customising column field names in GraphQL schema
* [docs] add custom column fields doc in API reference
* add tests
* rename 'ColField' to 'ColumnField'
* embed column's graphql field in 'PGColumnInfo'
-> Value constructor of 'PGCol' is not exposed
-> Using 'parseJSON' to construct 'PGCol' in 'FromJSON' instances
* avoid using 'Maybe TableConfig'
* refactors & 'custom_column_fields' -> 'custom_column_names'
* cli-test: add configuration field in metadata export test
* update expected keys in `FromJSON` instance of `TableMeta`
* use `buildSchemaCacheFor` to update configuration in v2 track_table
* remove 'GraphQLName' type and use 'isValidName' exposed from parser lib
* point graphql-parser-hs library git repo to hasura
* support 'set_table_custom_fields' query API & added docs and tests
* use positional arguments in SQL functions
* only allow omitting set of last arguments in functions
* disallow omitting of a non default argument in functions
* allow altering type of a column iff session vars are defined in permissions
* use a sum type to define dependency reason
* set jwt expiry test's expiry time to 4 seconds
* derive Data instance for necessary types to simplify 'hasStaticExp'
Currently, we allow tracking of a table with the same name as an already tracked function, and vice-versa. This causes an issue when querying from GraphQL since it will only query the table and not the function. I've made changes to disallow this by throwing an error.
1. Reuses postgres connections during startup which reduces the overhead of opening and closing connections.
2. Faster schema cache building. This is done by fetching all the required data in a single sql statement.
