Adding documentation for the standard library (FuelLabs#3314)

This PR aims to add documentation aswell as examples for more std
library functions

Example documentation
```
/// Inserts a key-value pair into the map.
/// 
/// # Arguments
///
/// * `key` - The key to which the value is paired
/// * `value` - The value to be stored
///
/// # Examples
/// 
/// ```
/// storage {
///     map: StorageMap = StorageMap {} 
/// }
/// 
/// fn foo() {
///     let key = 5_u64;
///     let value = true;
///     storage.map.insert(key, value);
///     let retrieved_value = storage.map.get(key);
///     assert(value == retrieved_value);
/// }
/// ```
#[storage(write)]
fn insert(self, key: K, value: V) {
    let key = sha256((key, __get_storage_key()));
    store::<V>(key, value);
}
```
closes FuelLabs#3313

Co-authored-by: Mohammad Fawaz <[email protected]>
Co-authored-by: Anton Trunov <[email protected]>

sway-lib-std/src/assert.sw

@@ -5,6 +5,24 @@ use ::revert::revert;
 /// Asserts that the given `condition` will always be `true` during runtime.
 /// To check for conditions that may not be `true`, use `std::revert::require` instead.
 /// See: https://en.wikipedia.org/wiki/Assertion_(software_development)#Comparison_with_error_handling
+///
+/// ### Arguments
+///
+/// * `condition` - The condition which will be asserted to be `true`
+///
+/// ### Reverts
+///
+/// Reverts when `condition` is `false`
+///
+/// ### Examples
+/// 
+/// ```sway
+/// fn foo(a: u64, b: u64) {
+///     assert(a == b);
+///     // if code execution continues, that means a was equal to b
+///     log("a is equal to b");
+/// }
+/// ```
 pub fn assert(condition: bool) {
     if !condition {
         revert(0);

sway-lib-std/src/message.sw

@@ -8,7 +8,7 @@ use ::error_signals::FAILED_SEND_MESSAGE_SIGNAL;
 
 /// Sends a message to `recipient` of length `msg_len` through `output` with amount of `coins`
 ///
-/// # Arguments
+/// ### Arguments
 ///
 /// * `recipient` - The address of the message recipient
 /// * `msg_data` - arbitrary length message data

sway-lib-std/src/revert.sw

@@ -6,11 +6,53 @@ use ::error_signals::FAILED_REQUIRE_SIGNAL;
 /// Context-dependent:
 /// will panic if used in a predicate
 /// will revert if used in a contract
+///
+/// ### Arguments
+///
+/// * `code` - The code with which to revert the program
+///
+/// ### Reverts
+///
+/// Reverts when called in a contract
+///
+/// ### Panics
+///
+/// Panics when called in a predicate
+///
+/// ### Examples
+/// 
+/// ```sway
+/// fn foo(should_revert: bool) {
+///     match should_revert {
+///         true => revert(0),
+///         false => {},
+///     }
+/// }
+/// ```
 pub fn revert(code: u64) {
     __revert(code)
 }
 
 /// Checks if the given `condition` is `true` and if not, logs `value` and reverts.
+///
+/// ### Arguments
+///
+/// * `condition` - The condition upon which to decide whether to revert or not
+/// * `value` - The value which will be logged in case `condition` is `false`
+///
+/// ### Reverts
+///
+/// Reverts when `condition` is false
+///
+/// ### Examples
+/// 
+/// ```sway
+/// fn foo(a: u64, b: u64) {
+///     require(a == b, "a was not equal to b");
+///     // If the condition was true, code execution will continue
+///     log("The require function did not revert");
+/// }
+/// ```
 pub fn require<T>(condition: bool, value: T) {
     if !condition {
         log(value);