Starting organizing code

Moved current page files (stock_info.c/h and stockwatch.c) to src/page
Will likely rename them to page_<name>.c/h

Added a few lines to .gitignore to not add the build folder (and .lock files)

The current plan (at least mine) is to organize the code as follows:
   Every 'class' (organization of code and data) has a .h and .c file
   The .h file defines functions to be used to interface with it (the API)
   The .c file has the following (in this order):
      static variable definitions
      static function prototypes
      API function (as declared in the .h) definitions
      static function definitions
   Maybe have a standard way to separate these sections?
   Every API function should be prefixed with the name of the 'class'
      So for example, to get a value from a struct called thing, call:
         thing_get_value(...)
   Except for simple structs (and static structs), prefer to call functions
      to get/set data from them rather than access the data yourself.
      This means make getter/setter functions in the API!
      Depending on the circumstance, getting data directly might be okay,
         but setting the data might be bad (as setters can check for validity)
   And finally, COMMENT THE CODE!