docs: More docs and improvements of existing docs

- Tried not to leave a single public function undocumented, though did not double-document public function with obvious names
- Remove all mentions of the strategy selector in favour of the strategy registry (to avoid confusion)

src/encoding/evm/swap_encoder/builder.rs

@@ -4,6 +4,7 @@ use crate::encoding::{
     swap_encoder::SwapEncoder,
 };
 
+/// Builds a `SwapEncoder` for the given protocol system and executor address.
 pub struct SwapEncoderBuilder {
     protocol_system: String,
     executor_address: String,

src/encoding/evm/swap_encoder/swap_encoder_registry.rs

@@ -7,12 +7,16 @@ use crate::encoding::{
     swap_encoder::SwapEncoder,
 };
 
+/// Registry containing all supported `SwapEncoders`.
 #[derive(Clone)]
 pub struct SwapEncoderRegistry {
+    /// A hashmap containing the protocol system as a key and the `SwapEncoder` as a value.
     encoders: HashMap<String, Box<dyn SwapEncoder>>,
 }
 
 impl SwapEncoderRegistry {
+    /// Populates the registry with the `SwapEncoders` for the given blockchain by parsing the
+    /// executors in the file at the given path.
     pub fn new(executors_file_path: &str, blockchain: Chain) -> Result<Self, EncodingError> {
         let config_str = fs::read_to_string(executors_file_path)?;
         let config: HashMap<Chain, HashMap<String, String>> = serde_json::from_str(&config_str)?;