graphLibrary -- constructs a graph of a type specified in the string input

i1 : G = graphLibrary("petersen")

o1 = Graph{0 => {1, 4, 5}}
           1 => {0, 2, 6}
           2 => {1, 3, 7}
           3 => {2, 4, 8}
           4 => {0, 3, 9}
           5 => {0, 7, 8}
           6 => {1, 8, 9}
           7 => {2, 5, 9}
           8 => {3, 5, 6}
           9 => {4, 6, 7}

o1 : Graph

i2 : G = graphLibrary("f26a")

o2 = Graph{0 => {1, 7, 25}   }
           1 => {0, 2, 20}
           2 => {1, 3, 9}
           3 => {2, 4, 22}
           4 => {3, 5, 11}
           5 => {4, 6, 24}
           6 => {5, 7, 13}
           7 => {0, 6, 8}
           8 => {7, 9, 15}
           9 => {2, 8, 10}
           10 => {9, 11, 17}
           11 => {4, 10, 12}
           12 => {11, 13, 19}
           13 => {6, 12, 14}
           14 => {13, 15, 21}
           15 => {8, 14, 16}
           16 => {15, 17, 23}
           17 => {10, 16, 18}
           18 => {17, 19, 25}
           19 => {12, 18, 20}
           20 => {1, 19, 21}
           21 => {14, 20, 22}
           22 => {3, 21, 23}
           23 => {16, 22, 24}
           24 => {5, 23, 25}
           25 => {0, 18, 24}

o2 : Graph

i3 : G = graphLibrary("chvatal")

o3 = Graph{0 => {1, 3, 6, 11} }
           1 => {0, 2, 4, 7}
           2 => {1, 3, 5, 8}
           3 => {0, 2, 4, 10}
           4 => {1, 3, 5, 9}
           5 => {2, 4, 6, 11}
           6 => {0, 5, 7, 9}
           7 => {1, 6, 8, 10}
           8 => {2, 7, 9, 11}
           9 => {4, 6, 8, 10}
           10 => {3, 7, 9, 11}
           11 => {0, 5, 8, 10}

o3 : Graph