Reduce Memory Usage by Optimizing Order of Fields

[gaby]

Optimized the order of fields in several structs, this results in a reduction of memory usage by quicktemplate.

Summary:

/quicktemplate/jsonstring.go:61:19: 256 bytes saved: struct with 264 pointer bytes could be 8
/quicktemplate/parser/parser.go:15:13: 8 bytes saved: struct of size 96 could be 88
/quicktemplate/parser/scanner.go:33:12: 8 bytes saved: struct with 16 pointer bytes could be 8
/quicktemplate/parser/scanner.go:53:14: 16 bytes saved: struct of size 192 could be 176
/quicktemplate/parser/scanner_test.go:325:9: 8 bytes saved: struct with 16 pointer bytes could be 8

[gaby]

@valyala Quick optimization that should reduce memory usage by around ~300 bytes.

I also submitted the same optimization to bytebufferpool valyala/bytebufferpool#29