hw5 spec
test1.asm: test assembly for function call, add lose grammar rule
finish function prologue and epilogue
finish codegen preparation for variable declaration.
implement register manager for expression codegen to allocate register
finish FP part in register manager
gen assignstmt finish, gen expr and sub functions finish 50%
modified register manager, AST place interface, and the code use their interface
add floating point codegen function, return stmt, rearrange order of function
finish getExprNode, interface genstmtlist, genstmt, gen assignexpr, genblock
add functionCallStmt, ConstStringSet struct for const string
add codegen for read/write function, modify main function
debug some error
fix compiler error, semanticAnalysis ignore builtin function write/read/fread