Fix/lp_solvePath

[adfeel220]

Fix LPSolve Path

Many users are reporting the problem with lp_solve, specifically with resolving the path to lp_solve executable that's linked to the usage of Panco. This fix introduces the following approaches to address issue #4.

• Introduce a small test upon initializing Saihu, and show a warning if lp_solve cannot be executed properly.
• A suggestion of how to install lp_solve is printed at the end of the warning according to the user's OS.
• Resolving the path for lp_solve is performed in the following order:
  1. Use the path written in saihu/resources/lpsolve
  2. Try to run which lp_solve and which lpsolve, and apply the result if any of them succeed.
  3. Look for the file in the program entry directory, i.e. ./lp_solve