modules: add ability to clear cache (#2300)

This adds the ability to remove a single module from the cache, or to
clear the entire module cache.

JerryScript-DCO-1.0-Signed-off-by: Gabriel Schulhof gabriel.schulhof@intel.com

docs/12.EXT-REFERENCE-MODULE.md

@@ -27,6 +27,11 @@ The purpose of having resolvers is to be able to account for the fact that diffe
 differently and thus, for each type of module a module resolver must be supplied at the point where an instance of that
 type of module is requested.
 
+Individual modules may be removed from the cache by calling `jerryx_module_clear_cache`. This function behaves
+identically to `jerryx_module_resolve` in that it first checks the cache for the requested module, except that it
+removes the module if found. Additionally, it clears the entire cache of all modules if called using a JavaScript value
+of `undefined` as its first parameter.
+
 Additionally, this extension provides a means of easily defining so-called "native" JerryScript modules which can be
 resolved using the native JerryScript module resolver `jerryx_module_native_resolver`, which can be passed to
 `jerryx_module_resolve()`. Native modules are registered during application startup and by calling `dlopen()` by means
@@ -56,7 +61,7 @@ to `jerryx_module_resolve` with a module name whose canonical name matches an al
 
 ```c
 jerry_value_t
-jerryx_module_resolve (const jerry_char_t *name,
+jerryx_module_resolve (const jerry_value_t name,
                        const jerryx_module_resolver_t *resolvers_p,
                        size_t resolver_count);
 ```
@@ -67,6 +72,26 @@ jerryx_module_resolve (const jerry_char_t *name,
 - return value - `jerry_value_t` representing the module that was loaded, or the error that occurred in the process.
 
 
+## jerryx_module_clear_cache
+
+**Summary**
+
+Remove a module from the current context's cache, or clear the cache entirely.
+
+**Prototype**
+
+```c
+void
+jerryx_module_clear_cache (const jerry_value_t name,
+                           const jerryx_module_resolver_t *resolvers_p,
+                           size_t resolver_count);
+```
+
+- `name` - the name of the module to remove from cache or a JavaScript `undefined` to clear the entire cache
+- `resolvers_p` - the list of resolvers to call in sequence
+- `resolver_count` - the number of resolvers in `resolvers_p`
+
+
 ## jerryx_module_native_resolver
 
 **Summary**