code-gen: flatten output

[dirkdev98]

Means less files that changed in Git diffs, and easier to use exports while still allowing tree-shaking.

BREAKING CHANGE: rewrite your references to validators or custom structure usage.

[github-actions]

==== C8 test coverage ====
Statements: 70.3% ( 17956/25542 )
Branches : 71.52% ( 2104 /2942 )
Functions : 70.69% ( 668 /945 )
Lines : 70.3% ( 17956 /25542 )

[github-actions]

==== Benchmark result ====

Node.js version: 15

Total benchmarks: 9
          Passed: 9
          Failed: 0
-----------
object validator simple      5000000  iterations     452  ns/op
object validator nested        50000  iterations   43503  ns/op
logger - strings              500000  iterations    2008  ns/op
logger - objects              500000  iterations    2690  ns/op
logger - deep objects         500000  iterations    4388  ns/op
uuid                         2000000  iterations     550  ns/op
uuid.isValid                10000000  iterations     148  ns/op
isNil                      500000000  iterations       0  ns/op
isPlainObject              100000000  iterations      16  ns/op

[github-actions]

==== Benchmark result ====

Node.js version: 14

Total benchmarks: 9
          Passed: 9
          Failed: 0
-----------
object validator simple      2000000  iterations     532  ns/op
object validator nested        50000  iterations   49269  ns/op
logger - strings              500000  iterations    2338  ns/op
logger - objects              500000  iterations    2747  ns/op
logger - deep objects         500000  iterations    4826  ns/op
uuid                         2000000  iterations     549  ns/op
uuid.isValid                10000000  iterations     173  ns/op
isNil                      500000000  iterations       0  ns/op
isPlainObject              100000000  iterations      20  ns/op

[github-actions]

==== C8 test coverage ====
Statements: 70.3% ( 17956/25542 )
Branches : 71.52% ( 2104 /2942 )
Functions : 70.69% ( 668 /945 )
Lines : 70.3% ( 17956 /25542 )