v0.38.0

Most relevant commits:

• compiler/ast: remove Import.Context field
• compiler/lexer: support JavaScript modules
• compiler: complete the implementation of the 'render' expression
• compiler/emitter: optimize Text instructions merging them into one
• templates: move MarkdownConverter option from run to build
• playground: update 'wasm_exec.js' with Go 1.16 version
• playground: update packages.go for Go 1.16
• compiler,runtime: allows the explicit conversion from markdown to html