reintroduced linkme() call in core_hal.c - or some of the interrupt handlers remain weak.

Without "linkme()" call in core_hal.c - notice the weak symbols

0800d8fd T BUTTON_EXTI_Config
080164dc T BUTTON_EXTI_LINE
20000280 D BUTTON_EXTI_TRIGGER
0800ebc5 T EXTI_ClearFlag
0800ebd1 T EXTI_ClearITPendingBit
0800eb41 T EXTI_Init
08005e81 W EXTI0_IRQHandler
08005e81 W EXTI1_IRQHandler
08005e81 W EXTI15_10_IRQHandler
08005e81 W EXTI2_IRQHandler
08005e81 W EXTI3_IRQHandler
08005e81 W EXTI4_IRQHandler
08005e81 W EXTI9_5_IRQHandler
0800ede1 T GPIO_EXTILineConfig

with:

0800e559 T BUTTON_EXTI_Config
08017cd4 T BUTTON_EXTI_LINE
20000288 D BUTTON_EXTI_TRIGGER
0800fa2d T EXTI_ClearFlag
0800fa55 T EXTI_ClearITPendingBit
0800fa39 T EXTI_GetITStatus
0800f9a9 T EXTI_Init
0800dbf1 T EXTI0_IRQHandler
0800dc11 T EXTI1_IRQHandler
0800dcf5 T EXTI15_10_IRQHandler
0800dc31 T EXTI2_IRQHandler
0800dc65 T EXTI3_IRQHandler
0800dc85 T EXTI4_IRQHandler
0800dca5 T EXTI9_5_IRQHandler
0800fc65 T GPIO_EXTILineConfig
0800cfcd T HAL_EXTI_Handler
0800e229 T SPI_EXTI_IntHandler
Merge remote-tracking branch 'spark/feature/hal' into brewpi
reformat tft libraries so netbeans code assistance works.