Improve the Parsing of NeoMutt Commands

Introduction

When a user enters a command, the string is first passed to parse_rc_line().

It uses macro SKIPWS() and function parse_extract_token() to extract the first 'token' -- the Command name.
parse_rc_line() uses command_find_by_name() which returns a struct Command.

Further work is delegated to a custom parsing function, found in Command.parse().

The custom parse functions use macros: MoreArgs(), MoreArgsF(), SKIPWS() and function parse_extract_token()
to extract the parameters for the Command.

About the Commands

Most of the Commands are defined in two places:

• MuttCommands in commands/commands.c
• HookCommands in hooks/commands.c

For each Command, struct Command contains:

• Name
• Description
• Prototype
• Parsing function
• Data

Problems

The macros work, but are hard to understand, hard to debug and hard to test.

MoreArgsF() was created to be a more nuanced version of MoreArgs().
It was felt that altering MoreArgs() to support other flags would likely break some existing parsing.

Tasks

1. Create tests for the macros: MoreArgs(), MoreArgsF() and SKIPWS()
   Use the existing code, and Command Prototypes, for inspiration.

2. Turn MoreArgs(), MoreArgsF() and SKIPWS() into functions
   Check the tests still work.

3. Merge the MoreArgs() and MoreArgsF() into a single function.
   Update the tests to match