fix some words' errors

complete semantic's introduction

add error handling to parser introduction

complete parser introduction

partial complete parser's introduction

finish lexer section

context-free grammar form

move grammar to single file, modify lexer.md

fix bug: crashes when calling a non-exists method

update readme.md

some intro for explicit field/method access

add toc for the file

change the inline span item to a item

combine two files to one file

rename blogs to docs