add element finder, so user can find possible lines within a certain range
add more doc
use six and move continue to next line
add test for element finder
fix bugs to support both lower and upper cases for element name
clean up
add line_near function in Element class
rm type checking
add property to do data protection
use function for element_find
update test file
remove setter
use dict only
change cs to return a function, the incident energy is take as an argument
make change in class Element for the issue of energy as argument
change license style
license updated for test files
change incident energy in test file and element_finder.py, also correct the doc
use six for test file
use capital Z, and use assert_equal in test file