enhance BuiltinFunction

toInt, toReal, toString, loadMatrix
did caching for loadMatrix in MatrixFactory
add more builtin functions

1. change usage of submat from (x1,x2,y1,y2) to (x1,y1,x2,y2)
2. change the syntax of sum. add builtin functions: colsum, rowsum,
matsum, explicit saying the way of summation
3. add logdet
4. add submat, getrow, getcol, getrows, getcols
remove unnecessary code
update linear-algebra.blog

merge linear-algebra2 and linear-algebra
update matrix construct functions

now it allows both 1 and 2 arguments
update matrix construct functions
swap the loop order of sumCols
update Linear-Algebra.blog
fix bug in buildin function
add loadRealMatrix()
Merge pull request #306 from BayesianLogic/Enhance-Builtin-Functions

enhance BuiltinFunction