add memo program (anza-xyz#105)

* add memo program

* use MAX_CPI_ACCOUNTS over MAX_TX_ACCOUNTS

* nit

* add account info borrowing check

* update docstring and comments

* use &str over &[u8]

* check num_accounts

* avoid unnecessary codegen

* update doc to use &str over &[u8]

* fix doc

* seperate lifetime

Author: publicqi

instruction-view/src/cpi.rs

@@ -11,7 +11,7 @@ use crate::{
 };
 
 /// Maximum number of accounts that can be passed to a cross-program invocation.
-const MAX_CPI_ACCOUNTS: usize = 64;
+pub const MAX_CPI_ACCOUNTS: usize = 64;
 
 /// An `Instruction` as expected by `sol_invoke_signed_c`.
 ///