Add configuration of max process memory chunk

The YR_CONFIG_MAX_PROCESS_MEMORY_CHUNK configuration is missing from yara-rust. However, there is a big issue when trying to add it, it's that this configuration uses a u64 value, while all other configs uses a u32.

The current design only works with u32s, where the get_configuration & set_configuration are generic over a config enum, and always retrieve/uses a u32 value.

To add a config that uses a u64 value, there are several possibilities:

Use the same API as YARA: add a get/set_configuration_u32 and a get/set_configuration_u64, both returning an error when not providing the right configuration. I'm not a fan, this doesn't look very rusty at all
Use something like this:

enum ConfigToSet {
   MaxMatchData(u32),
   MaxProcessMemoryChunk(u64),
}

enum Config {
   MaxMatchData,
   MaxProcessMemoryChunk,
}
enum ConfigValue {
    U32(u32),
    U64(u64),
}

pub fn get_config(Config) -> Result<ConfigValue>;
pub fn set_config(ConfigToSet) -> Result<()>;

or something of that effect

Create helpers for each config, using the right value type. This is the design I used.

Main issue is that it breaks backward compat, and it is very verbose. For the moment (and I don't suspect it will change), there is only 4 config parameters, so the verbosity is not that high.

Let me know what you think

Hugal31 / yara-rust

Add configuration of max process memory chunk #111