#include "Timer.h"

Timer t;
int pin = 13;

void setup()
  pinMode(pin, OUTPUT);
  t.oscillate(pin, 100, LOW);
  t.every(1000, takeReading)

void loop()

void takeReading(void* context)

there is an error (no matching function for call to 'Timer::every(int, void (&)(void*))')


Looking at the prototype in timer.h, it appears that the callback function can takes arguments:

int8_t every(unsigned long period, void (*callback)(void));

You're trying to make it take a void *.