Support complex initializers

[ShivamSarodia]

Today, only initializers of integral and pointer types declared locally is supported by ShivyC. In particular, the following are unsupported:

• Initialization of an array, like int a[2] = {1, 2};
• Initialization of a string, like char s[3] = "hi";

This will require some frontend changes in the parser and some backend changes to load the initialization values into the variables.

[ShivamSarodia]

May pair well with #68