Optimise iteration and lookups

[mikee47]

This PR improves performance of object iteration and indexing.

For example, calling indexOf on an Array<uint32_t> object results in repeated calls to the data() method.
Further, the C++ iterator implementation does the same.

A new speed test module has been added to evaulate performance. This uses some moderately large test objects and evaluates how long it takes to iterate through them using three methods:

1. regular for(unsigned i=0; i<array.count(); ++i) loop
2. C++ iterator for(auto: array)
3. Using the indexOf method

Array has 1000 elements.
Vector has 367 elements, referencing 3208 bytes of string data.
Map<int, String> has 367 elements.

These are the results, in microseconds, on an esp8266:

Operation	Current	With this PR
Array for-loop	1603	1611
Array iterator	1326	403
Array.indexOf	1303	425
Vector for-loop	800	721
Vector iterator	774	402
Vector indexOf(const char*)	6634	969
Vector indexOf(String)	849	476
Map<int, String> for-loop	1042	1085
Map<int, String> iterator	891	577
Map<int, String> indexOf	189	189
Map<int, String> lookup	168	168

Optimise iteration and indexOf operation

The regular [] operator and valueAt methods include range checks which are costly inside a loop.
Adding unsafe methods skips these checks.

Improve Vector search for char argument*

The indexOf method has been specialised for char* arguments so that strlen() only needs to be called once. Previously it was called on every loop iteration.

Provide base == operator which does binary comparison

This allows easy searching by value (object content).

Rationalise string comparison methods

FlashStrings have three equals overloads for char*, String and FlashString arguments.
We also require three equalsignorecase equivalents and appropriate operator== implementations.

By adding an ignoreCase parameter to all three equals methods we can simplify code.

Other improvements

• Use const references instead of copy
• Move copy/invalidate operations to constructors
• Use constexpr where possible for method return values
• Move printElement(Print, char) specialization into source file
• Move read method out of header
• Add github workflow
• Put strings in flash

[mikee47]

Note: Squash commit deleted in favour of branch merge.