Add show_histograms argument to display histograms (and clip_histograms for clipping outliers).

[tompollard]

This pull request adds two new arguments to address #132:

    show_histograms : bool, default=False
        Whether to include mini-histograms for continuous variables.
    clip_histograms : tuple or None, default (1, 99)
        If show_histograms=True, specify a (lower_percentile, upper_percentile) range to clip the
        data before generating histograms. This reduces the influence of extreme outliers.
        For example, (1, 99) clips to the 1st and 99th percentiles.
        Set to None to disable clipping and use the full range of values.

When show_histograms is set to True, histograms will be added at the end of the table. A simple example is shown below:

from tableone import TableOne, load_dataset

data = load_dataset('pn2012')
table1 = TableOne(data, show_histograms=True)
print(table1.tabulate(tablefmt="rounded_outline"))

╭───────────────────┬──────┬───────────┬──────────────┬─────────────╮
│                   │      │ Missing   │ Overall      │ Histogram   │
├───────────────────┼──────┼───────────┼──────────────┼─────────────┤
│ n                 │      │           │ 1000         │             │
│ Age, mean (SD)    │      │ 0         │ 65.0 (17.2)  │ ▂▂▃▄▆▇█▇    │
│ SysABP, mean (SD) │      │ 291       │ 114.3 (40.2) │ ▂▁▁▃█▆▃▁    │
│ Height, mean (SD) │      │ 475       │ 170.1 (22.1) │ ▁▃▅▇▇█▂▁    │
│ Weight, mean (SD) │      │ 302       │ 82.9 (23.8)  │ ▃▆█▆▄▃▁▁    │
│ ICU, n (%)        │ CCU  │           │ 162 (16.2)   │             │
│                   │ CSRU │           │ 202 (20.2)   │             │
│                   │ MICU │           │ 380 (38.0)   │             │
│                   │ SICU │           │ 256 (25.6)   │             │
│ MechVent, n (%)   │ 0    │           │ 540 (54.0)   │             │
│                   │ 1    │           │ 460 (46.0)   │             │
│ LOS, mean (SD)    │      │ 0         │ 14.2 (14.2)  │ █▆▃▁▁▁▁▁    │
│ death, n (%)      │ 0    │           │ 864 (86.4)   │             │
│                   │ 1    │           │ 136 (13.6)   │             │
╰───────────────────┴──────┴───────────┴──────────────┴─────────────╯

An example of a stratified table is below:

╭───────────────────┬──────┬───────────┬──────────────┬──────────────┬───────────────┬───────────────┬─────────────────────╮
│                   │      │ Missing   │ 0            │ 1            │ 0 Histogram   │ 1 Histogram   │ Overall Histogram   │
├───────────────────┼──────┼───────────┼──────────────┼──────────────┼───────────────┼───────────────┼─────────────────────┤
│ n                 │      │           │ 864          │ 136          │               │               │                     │
│ Age, mean (SD)    │      │ 0         │ 64.0 (17.4)  │ 71.7 (14.0)  │ ▂▂▄▄▆▇█▇      │ ▁▂▃▄▄▆██      │ ▂▂▃▄▆▇█▇            │
│ SysABP, mean (SD) │      │ 291       │ 115.4 (38.3) │ 107.6 (49.4) │ ▂▁▁▂█▇▄▁      │ ▄▁▂▆██▄▂      │ ▂▁▁▃█▆▃▁            │
│ Height, mean (SD) │      │ 475       │ 170.3 (23.2) │ 168.5 (11.3) │ ▁▂▆▇▇█▂▁      │ ▂▆▄▅█▄▅▆      │ ▁▃▅▇▇█▂▁            │
│ Weight, mean (SD) │      │ 302       │ 83.0 (23.6)  │ 82.3 (25.4)  │ ▂▆█▆▄▂▁▁      │ ▅▇█▅▃▄▁▂      │ ▃▆█▆▄▃▁▁            │
│ ICU, n (%)        │ CCU  │           │ 137 (15.9)   │ 25 (18.4)    │               │               │                     │
│                   │ CSRU │           │ 194 (22.5)   │ 8 (5.9)      │               │               │                     │
│                   │ MICU │           │ 318 (36.8)   │ 62 (45.6)    │               │               │                     │
│                   │ SICU │           │ 215 (24.9)   │ 41 (30.1)    │               │               │                     │
╰───────────────────┴──────┴───────────┴──────────────┴──────────────┴───────────────┴───────────────┴─────────────────────╯