NLSolversBase introduction

Merge pull request #37 from JuliaNLSolvers/newdf2

Use NLSolversBase

Fix bug in backtracking cubic interpolation

Merge pull request #30 from anriseth/updatelsr

Store morethuente step info in lsr

Add `basic!` algorithm

Merge pull request #26 from anriseth/basic

Add basic linesearch

v0.1.3: Merge pull request #23 from anriseth/initialstep

Make initial step length a parameter for morethuente and strongwolfe