Some const correctness fixes

Vector.h

@@ -53,7 +53,7 @@ class Vector {
 
     // Equals Operator: Returns true if the number of elements is identical and
     // each of these elements are equal
-    bool operator==(const Vector &other) {
+    bool operator==(const Vector &other) const {
         if (size() != other.size()) return false;
 
         for (unsigned int i = 0; i < size(); i++) {
@@ -105,7 +105,7 @@ class Vector {
         }
     }
 
-    T *as_array() {
+    T *as_array() const {
         return data;
     }
 
@@ -172,19 +172,19 @@ class Vector {
 
     // Return a sensible capacity for the given size (including some
     // padding).
-    unsigned int get_capacity_for_size(unsigned int size) {
+    unsigned int get_capacity_for_size(unsigned int size) const {
         return size * 2 + 5;
     }
 
     // Return true if the Vector is holding much more memory (capacity) than it
     // currently needs (element_count).
-    inline bool is_using_excessive_memory() {
+    inline bool is_using_excessive_memory() const {
         return 10 + element_count * 2 < capacity;
     }
 
     // Return true if the passed new_size would cause the Vector to exceed the
     // current capacity (meaning it must be expanded with `reallocate` first).
-    inline bool new_size_exceeds_capacity(unsigned int new_size) {
+    inline bool new_size_exceeds_capacity(unsigned int new_size) const {
         return new_size > capacity;
     }