nop - no-op
newobj - create an object and call its constructor.
stloc.0 - Pop a value from the stack, and store it in the first local variable
ldloc.0 - Push the first local variable onto the stack
ret - return
ldarg.0 - Push the first argument (this in instance methods) onto the stack
ldstr - Push a string onto the stack
stfld - set the field, using data on the stack.
ldc.i4.s - Push the specified number as an int.
.ctor - constructor
在wiki找到一个很全的IL指令对码表，在这里记录下来，方便对照。
https://en.wikipedia.org/wiki/List_of_CIL_instructions
