Here is a list of all files with brief descriptions:

src
eastasianwidthdata.c
eastasianwidthdef.c
eastasianwidthdef.h
emojidata.c
emojidef.c	Emoji-related routine and data that are used internally
emojidef.h	Definitions of internal data structure and function for extended pictographs
graphemebreak.c	Implementation of the grapheme breaking algorithm as described in Unicode Standard Annex 29
graphemebreak.h	Header file for the grapheme breaking algorithm
graphemebreakdata.c
graphemebreakdef.h	Definitions of internal data structures, declarations of global variables, and function prototypes for the grapheme breaking algorithm
indicconjunctbreakdata.c
indicconjunctbreakdef.h
linebreak.c	Implementation of the line breaking algorithm as described in Unicode Standard Annex 14
linebreak.h	Header file for the line breaking algorithm
linebreakauxdata.c
linebreakdata.c
linebreakdef.c	Definition of language-specific data
linebreakdef.h	Definitions of internal data structures, declarations of global variables, and function prototypes for the line breaking algorithm
test_skips.h
unibreakbase.c	Definition of basic libunibreak information
unibreakbase.h	Header file for common definitions in the libunibreak library
unibreakdef.c	Definition of utility functions used by the libunibreak library
unibreakdef.h	Header file for private definitions in the libunibreak library
wordbreak.c	Implementation of the word breaking algorithm as described in Unicode Standard Annex 29
wordbreak.h	Header file for the word breaking (segmentation) algorithm
wordbreakdata.c
wordbreakdef.h	Definitions of internal data structures, declarations of global variables, and function prototypes for the word breaking algorithm