WIP: add asv benchmarks

[ev-br]

• PySparse ll_mat
• CJ's sparray
• fast_lil_matrix (ENH: sparse: add fast_lil_matrix sparse matrix scipy/scipy#6004)

[ev-br]

(scipy_np_1002)br@duneyrr:~/sweethome/proj/scipy/sparr/benchmarks$ asv run --python=same -e
· Discovering benchmarks
· Running 3 total benchmarks (1 commits * 1 environments * 3 benchmarks)
[  0.00%] ·· Building for /home/br/virtualenvs/scipy_np_1002/bin/python
[  0.00%] ·· Benchmarking /home/br/virtualenvs/scipy_np_1002/bin/python
[ 33.33%] ··· Running benchmarks.BenchPoisson2D.mem_poisson2d                                                                                                                ok
[ 33.33%] ···· 
               ===== =========== ======== ========== ============
               --                       class                    
               ----- --------------------------------------------
                 n    map_array   ll_mat   fast_lil   dok_matrix 
               ===== =========== ======== ========== ============
                 10      0.0       0.0       0.0         0.0     
                100      0.0       0.0       0.0         0.0     
                300      0.0       0.0       0.0         0.0     
               ===== =========== ======== ========== ============

[ 66.67%] ··· Running benchmarks.BenchPoisson2D.peakmem_poisson2d                                                                                                            ok
[ 66.67%] ···· 
               ===== =========== ======== ========== ============
               --                       class                    
               ----- --------------------------------------------
                 n    map_array   ll_mat   fast_lil   dok_matrix 
               ===== =========== ======== ========== ============
                 10       19M       19M       19M         19M    
                100       25M       20M       21M         28M    
                300       69M       27M       35M         99M    
               ===== =========== ======== ========== ============

[100.00%] ··· Running benchmarks.BenchPoisson2D.time_poisson2d                                                                                                               ok
[100.00%] ···· 
               ===== =========== ========= ========== ============
               --                        class                    
               ----- ---------------------------------------------
                 n    map_array    ll_mat   fast_lil   dok_matrix 
               ===== =========== ========= ========== ============
                 10    311.51μs   78.28μs   801.11μs     4.93ms   
                100    39.28ms     7.98ms   80.66ms     563.96ms  
                300    378.91ms   75.55ms   766.65ms     5.01s    
               ===== =========== ========= ========== ============