Amendments to Limit Evaluation and Series Expansion

SymPy is a Python library for symbolic mathematics. SymPy has a powerful "series" module, which is the backbone of all the limit evaluations performed by the library. A drawback is that the limit evaluation is highly dependent on the Gruntz algorithm making it inefficient, because of the highly recursive nature of the algorithm. Hence, the aim of this project is to improve the performance (speeding-up) of limit evaluation, by reducing the dependency on the Gruntz algorithm and implementing a structured way to evaluate limits. A structured implementation will make it easy to debug, in case of any wrong evaluation, depending on the type of function present in the limit expression.